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 $235.95   10.490%   $260.7012   $260.70   $260.70   $260.70  
  Purchase #2 $90.40   5.285%   $95.1776   $95.18   $95.20   $95.20  
  Purchase #3 $57.67   12.597%   $64.9347   $64.93   $64.95   $64.90  
  Purchase #4 $186.80   4.634%   $195.4563   $195.46   $195.45   $195.50  
  Purchase #5 $9.58   10.542%   $10.5899   $10.59   $10.60   $10.60  
  Purchase #6 $64.34   3.727%   $66.738   $66.74   $66.75   $66.70  
  Purchase #7 $225.47   11.286%   $250.9165   $250.92   $250.90   $250.90  
  7 purchase totals = $870.21       $944.5142   $944.52   $944.55   $944.50