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 $53.48   9.157%   $58.3772   $58.38   $58.40   $58.40  
  Purchase #2 $104.40   12.577%   $117.5304   $117.53   $117.55   $117.50  
  Purchase #3 $191.77   12.211%   $215.187   $215.19   $215.20   $215.20  
  Purchase #4 $195.39   5.481%   $206.0993   $206.10   $206.10   $206.10  
  Purchase #5 $218.65   7.715%   $235.5188   $235.52   $235.50   $235.50  
  Purchase #6 $44.81   9.180%   $48.9236   $48.92   $48.90   $48.90  
  Purchase #7 $63.56   9.373%   $69.5175   $69.52   $69.50   $69.50  
  7 purchase totals = $872.06       $951.1538   $951.16   $951.15   $951.10