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 $84.91   9.490%   $92.968   $92.97   $92.95   $93.00  
  Purchase #2 $139.85   9.799%   $153.5539   $153.55   $153.55   $153.60  
  Purchase #3 $7.96   8.782%   $8.659   $8.66   $8.65   $8.70  
  Purchase #4 $105.53   13.104%   $119.3587   $119.36   $119.35   $119.40  
  Purchase #5 $24.77   13.427%   $28.0959   $28.10   $28.10   $28.10  
  Purchase #6 $173.94   5.307%   $183.171   $183.17   $183.15   $183.20  
  Purchase #7 $20.26   7.233%   $21.7254   $21.73   $21.75   $21.70  
  7 purchase totals = $557.22       $607.5319   $607.54   $607.50   $607.70