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 $91.27   8.268%   $98.8162   $98.82   $98.80   $98.80  
  Purchase #2 $213.53   10.627%   $236.2218   $236.22   $236.20   $236.20  
  Purchase #3 $64.48   13.352%   $73.0894   $73.09   $73.10   $73.10  
  Purchase #4 $77.26   12.819%   $87.164   $87.16   $87.15   $87.20  
  Purchase #5 $68.79   13.492%   $78.0711   $78.07   $78.05   $78.10  
  Purchase #6 $11.65   4.387%   $12.1611   $12.16   $12.15   $12.20  
  Purchase #7 $133.54   5.127%   $140.3866   $140.39   $140.40   $140.40  
  7 purchase totals = $660.52       $725.9102   $725.91   $725.85   $726.00