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 $244.97   6.658%   $261.2801   $261.28   $261.30   $261.30  
  Purchase #2 $178.92   4.815%   $187.535   $187.54   $187.55   $187.50  
  Purchase #3 $222.48   13.850%   $253.2935   $253.29   $253.30   $253.30  
  Purchase #4 $89.50   3.114%   $92.287   $92.29   $92.30   $92.30  
  Purchase #5 $146.95   8.658%   $159.6729   $159.67   $159.65   $159.70  
  Purchase #6 $65.57   12.291%   $73.6292   $73.63   $73.65   $73.60  
  Purchase #7 $213.90   11.524%   $238.5498   $238.55   $238.55   $238.50  
  7 purchase totals = $1,162.29       $1,266.2475   $1,266.25   $1,266.30   $1,266.20