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 $169.39   8.455%   $183.7119   $183.71   $183.70   $183.70  
  Purchase #2 $126.78   6.170%   $134.6023   $134.60   $134.60   $134.60  
  Purchase #3 $68.88   9.287%   $75.2769   $75.28   $75.30   $75.30  
  Purchase #4 $140.94   8.763%   $153.2906   $153.29   $153.30   $153.30  
  Purchase #5 $7.63   11.449%   $8.5036   $8.50   $8.50   $8.50  
  Purchase #6 $76.71   10.810%   $85.0024   $85.00   $85.00   $85.00  
  Purchase #7 $183.60   5.212%   $193.1692   $193.17   $193.15   $193.20  
  7 purchase totals = $773.93       $833.5569   $833.55   $833.55   $833.60