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 $54.80   11.740%   $61.2335   $61.23   $61.25   $61.20  
  Purchase #2 $110.34   13.576%   $125.3198   $125.32   $125.30   $125.30  
  Purchase #3 $44.61   12.184%   $50.0453   $50.05   $50.05   $50.00  
  Purchase #4 $133.97   9.114%   $146.18   $146.18   $146.20   $146.20  
  Purchase #5 $229.75   12.562%   $258.6112   $258.61   $258.60   $258.60  
  Purchase #6 $158.79   6.187%   $168.6143   $168.61   $168.60   $168.60  
  Purchase #7 $89.59   9.746%   $98.3214   $98.32   $98.30   $98.30  
  7 purchase totals = $821.85       $908.3255   $908.32   $908.30   $908.20