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 $90.68   7.346%   $97.3414   $97.34   $97.35   $97.30  
  Purchase #2 $208.38   7.796%   $224.6253   $224.63   $224.65   $224.60  
  Purchase #3 $60.50   11.758%   $67.6136   $67.61   $67.60   $67.60  
  Purchase #4 $185.79   6.490%   $197.8478   $197.85   $197.85   $197.80  
  Purchase #5 $101.58   8.397%   $110.1097   $110.11   $110.10   $110.10  
  Purchase #6 $44.67   10.639%   $49.4224   $49.42   $49.40   $49.40  
  Purchase #7 $12.66   4.143%   $13.1845   $13.18   $13.20   $13.20  
  7 purchase totals = $704.26       $760.1447   $760.14   $760.15   $760.00