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 $167.95   9.362%   $183.6735   $183.67   $183.65   $183.70  
  Purchase #2 $143.31   9.443%   $156.8428   $156.84   $156.85   $156.80  
  Purchase #3 $67.66   11.815%   $75.654   $75.65   $75.65   $75.70  
  Purchase #4 $186.47   9.828%   $204.7963   $204.80   $204.80   $204.80  
  Purchase #5 $216.97   13.776%   $246.8598   $246.86   $246.85   $246.90  
  Purchase #6 $75.52   10.260%   $83.2684   $83.27   $83.25   $83.30  
  Purchase #7 $221.32   6.691%   $236.1285   $236.13   $236.15   $236.10  
  7 purchase totals = $1,079.20       $1,187.2233   $1,187.22   $1,187.20   $1,187.30