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 $33.99   5.247%   $35.7735   $35.77   $35.75   $35.80  
  Purchase #2 $217.97   3.125%   $224.7816   $224.78   $224.80   $224.80  
  Purchase #3 $191.35   11.605%   $213.5562   $213.56   $213.55   $213.60  
  Purchase #4 $220.57   11.621%   $246.2024   $246.20   $246.20   $246.20  
  Purchase #5 $136.75   11.249%   $152.133   $152.13   $152.15   $152.10  
  Purchase #6 $61.68   5.357%   $64.9842   $64.98   $65.00   $65.00  
  Purchase #7 $22.85   13.602%   $25.9581   $25.96   $25.95   $26.00  
  7 purchase totals = $885.16       $963.3890   $963.38   $963.40   $963.50