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 $183.55   11.684%   $204.996   $205.00   $205.00   $205.00  
  Purchase #2 $68.27   11.345%   $76.0152   $76.02   $76.00   $76.00  
  Purchase #3 $146.50   8.761%   $159.3349   $159.33   $159.35   $159.30  
  Purchase #4 $193.63   8.599%   $210.2802   $210.28   $210.30   $210.30  
  Purchase #5 $248.39   11.321%   $276.5102   $276.51   $276.50   $276.50  
  Purchase #6 $124.47   9.865%   $136.749   $136.75   $136.75   $136.70  
  Purchase #7 $178.53   7.481%   $191.8858   $191.89   $191.90   $191.90  
  7 purchase totals = $1,143.34       $1,255.7713   $1,255.78   $1,255.80   $1,255.70