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 $191.63   11.467%   $213.6042   $213.60   $213.60   $213.60  
  Purchase #2 $78.97   12.354%   $88.726   $88.73   $88.75   $88.70  
  Purchase #3 $8.73   10.557%   $9.6516   $9.65   $9.65   $9.70  
  Purchase #4 $207.94   7.177%   $222.8639   $222.86   $222.85   $222.90  
  Purchase #5 $92.41   9.182%   $100.8951   $100.90   $100.90   $100.90  
  Purchase #6 $27.75   11.362%   $30.903   $30.90   $30.90   $30.90  
  Purchase #7 $69.28   8.211%   $74.9686   $74.97   $74.95   $75.00  
  7 purchase totals = $676.71       $741.6124   $741.61   $741.60   $741.70