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 $119.66   11.781%   $133.7571   $133.76   $133.75   $133.80  
  Purchase #2 $16.40   10.193%   $18.0717   $18.07   $18.05   $18.10  
  Purchase #3 $104.26   11.370%   $116.1144   $116.11   $116.10   $116.10  
  Purchase #4 $109.82   8.124%   $118.7418   $118.74   $118.75   $118.70  
  Purchase #5 $46.58   3.787%   $48.344   $48.34   $48.35   $48.30  
  Purchase #6 $62.67   11.197%   $69.6872   $69.69   $69.70   $69.70  
  Purchase #7 $115.55   5.787%   $122.2369   $122.24   $122.25   $122.20  
  7 purchase totals = $574.94       $626.9531   $626.95   $626.95   $626.90