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 $101.90   13.858%   $116.0213   $116.02   $116.00   $116.00  
  Purchase #2 $192.79   11.648%   $215.2462   $215.25   $215.25   $215.20  
  Purchase #3 $217.44   13.527%   $246.8531   $246.85   $246.85   $246.90  
  Purchase #4 $247.63   12.612%   $278.8611   $278.86   $278.85   $278.90  
  Purchase #5 $48.50   12.158%   $54.3966   $54.40   $54.40   $54.40  
  Purchase #6 $98.64   3.383%   $101.977   $101.98   $102.00   $102.00  
  Purchase #7 $115.34   5.596%   $121.7944   $121.79   $121.80   $121.80  
  7 purchase totals = $1,022.24       $1,135.1497   $1,135.15   $1,135.15   $1,135.20