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 $87.77   8.555%   $95.2787   $95.28   $95.30   $95.30  
  Purchase #2 $213.77   10.376%   $235.9508   $235.95   $235.95   $236.00  
  Purchase #3 $138.74   5.682%   $146.6232   $146.62   $146.60   $146.60  
  Purchase #4 $65.85   7.510%   $70.7953   $70.80   $70.80   $70.80  
  Purchase #5 $235.97   13.344%   $267.4578   $267.46   $267.45   $267.50  
  Purchase #6 $135.90   11.632%   $151.7079   $151.71   $151.70   $151.70  
  Purchase #7 $105.90   9.867%   $116.3492   $116.35   $116.35   $116.30  
  7 purchase totals = $983.90       $1,084.1629   $1,084.17   $1,084.15   $1,084.20