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 $209.81   11.437%   $233.806   $233.81   $233.80   $233.80  
  Purchase #2 $135.45   9.607%   $148.4627   $148.46   $148.45   $148.50  
  Purchase #3 $63.93   3.641%   $66.2577   $66.26   $66.25   $66.30  
  Purchase #4 $50.54   8.786%   $54.9804   $54.98   $55.00   $55.00  
  Purchase #5 $46.75   3.154%   $48.2245   $48.22   $48.20   $48.20  
  Purchase #6 $124.91   6.536%   $133.0741   $133.07   $133.05   $133.10  
  Purchase #7 $176.77   7.821%   $190.5952   $190.60   $190.60   $190.60  
  7 purchase totals = $808.16       $875.4006   $875.40   $875.35   $875.50