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 $82.91   13.328%   $93.9602   $93.96   $93.95   $94.00  
  Purchase #2 $16.38   12.316%   $18.3974   $18.40   $18.40   $18.40  
  Purchase #3 $91.65   13.392%   $103.9238   $103.92   $103.90   $103.90  
  Purchase #4 $203.94   11.759%   $227.9213   $227.92   $227.90   $227.90  
  Purchase #5 $126.47   9.383%   $138.3367   $138.34   $138.35   $138.30  
  Purchase #6 $93.53   10.546%   $103.3937   $103.39   $103.40   $103.40  
  Purchase #7 $236.33   12.367%   $265.5569   $265.56   $265.55   $265.60  
  7 purchase totals = $851.21       $951.4900   $951.49   $951.45   $951.50