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 $110.85   12.463%   $124.6652   $124.67   $124.65   $124.70  
  Purchase #2 $229.63   6.845%   $245.3482   $245.35   $245.35   $245.30  
  Purchase #3 $216.41   13.389%   $245.3851   $245.39   $245.40   $245.40  
  Purchase #4 $62.71   10.744%   $69.4476   $69.45   $69.45   $69.40  
  Purchase #5 $101.70   10.489%   $112.3673   $112.37   $112.35   $112.40  
  Purchase #6 $89.41   12.838%   $100.8885   $100.89   $100.90   $100.90  
  Purchase #7 $235.71   12.313%   $264.733   $264.73   $264.75   $264.70  
  7 purchase totals = $1,046.42       $1,162.8349   $1,162.85   $1,162.85   $1,162.80