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 $73.26   13.700%   $83.2966   $83.30   $83.30   $83.30  
  Purchase #2 $69.45   8.131%   $75.097   $75.10   $75.10   $75.10  
  Purchase #3 $40.31   6.285%   $42.8435   $42.84   $42.85   $42.80  
  Purchase #4 $214.68   13.802%   $244.3101   $244.31   $244.30   $244.30  
  Purchase #5 $198.28   5.777%   $209.7346   $209.73   $209.75   $209.70  
  Purchase #6 $250.45   5.177%   $263.4158   $263.42   $263.40   $263.40  
  Purchase #7 $210.78   5.338%   $222.0314   $222.03   $222.05   $222.00  
  7 purchase totals = $1,057.21       $1,140.7290   $1,140.73   $1,140.75   $1,140.60