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 $236.55   13.545%   $268.5907   $268.59   $268.60   $268.60  
  Purchase #2 $87.42   5.316%   $92.0672   $92.07   $92.05   $92.10  
  Purchase #3 $134.40   10.145%   $148.0349   $148.03   $148.05   $148.00  
  Purchase #4 $204.85   5.171%   $215.4428   $215.44   $215.45   $215.40  
  Purchase #5 $143.72   8.408%   $155.804   $155.80   $155.80   $155.80  
  Purchase #6 $5.40   13.105%   $6.1077   $6.11   $6.10   $6.10  
  Purchase #7 $52.37   10.737%   $57.993   $57.99   $58.00   $58.00  
  7 purchase totals = $864.71       $944.0403   $944.03   $944.05   $944.00