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 $104.63   7.591%   $112.5725   $112.57   $112.55   $112.60  
  Purchase #2 $175.33   13.708%   $199.3642   $199.36   $199.35   $199.40  
  Purchase #3 $69.98   8.823%   $76.1543   $76.15   $76.15   $76.20  
  Purchase #4 $148.76   8.315%   $161.1294   $161.13   $161.15   $161.10  
  Purchase #5 $172.55   8.110%   $186.5438   $186.54   $186.55   $186.50  
  Purchase #6 $222.64   5.796%   $235.5442   $235.54   $235.55   $235.50  
  Purchase #7 $75.29   8.225%   $81.4826   $81.48   $81.50   $81.50  
  7 purchase totals = $969.18       $1,052.7910   $1,052.77   $1,052.80   $1,052.80