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 $84.95   10.254%   $93.6608   $93.66   $93.65   $93.70  
  Purchase #2 $102.38   3.463%   $105.9254   $105.93   $105.95   $105.90  
  Purchase #3 $209.27   3.496%   $216.5861   $216.59   $216.60   $216.60  
  Purchase #4 $56.38   11.348%   $62.778   $62.78   $62.80   $62.80  
  Purchase #5 $192.35   11.660%   $214.778   $214.78   $214.80   $214.80  
  Purchase #6 $150.79   5.533%   $159.1332   $159.13   $159.15   $159.10  
  Purchase #7 $53.57   12.319%   $60.1693   $60.17   $60.15   $60.20  
  7 purchase totals = $849.69       $913.0308   $913.04   $913.10   $913.10