Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $161.97   11.762%   $181.0209   $181.02   $181.00   $181.00  
  Purchase #2 $164.45   5.317%   $173.1938   $173.19   $173.20   $173.20  
  Purchase #3 $147.42   13.803%   $167.7684   $167.77   $167.75   $167.80  
  Purchase #4 $201.25   7.418%   $216.1787   $216.18   $216.20   $216.20  
  Purchase #5 $20.75   11.476%   $23.1313   $23.13   $23.15   $23.10  
  Purchase #6 $109.53   3.621%   $113.4961   $113.50   $113.50   $113.50  
  Purchase #7 $167.91   11.314%   $186.9073   $186.91   $186.90   $186.90  
  7 purchase totals = $973.28       $1,061.6965   $1,061.70   $1,061.70   $1,061.70