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 $244.53   9.413%   $267.5476   $267.55   $267.55   $267.50  
  Purchase #2 $58.43   12.343%   $65.642   $65.64   $65.65   $65.60  
  Purchase #3 $18.43   11.144%   $20.4838   $20.48   $20.50   $20.50  
  Purchase #4 $30.33   11.276%   $33.75   $33.75   $33.75   $33.80  
  Purchase #5 $64.87   13.858%   $73.8597   $73.86   $73.85   $73.90  
  Purchase #6 $73.63   9.267%   $80.4533   $80.45   $80.45   $80.50  
  Purchase #7 $119.31   11.455%   $132.977   $132.98   $133.00   $133.00  
  7 purchase totals = $609.53       $674.7134   $674.71   $674.75   $674.80