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 $75.66   11.557%   $84.404   $84.40   $84.40   $84.40  
  Purchase #2 $232.98   9.636%   $255.43   $255.43   $255.45   $255.40  
  Purchase #3 $162.71   6.757%   $173.7043   $173.70   $173.70   $173.70  
  Purchase #4 $210.74   6.521%   $224.4824   $224.48   $224.50   $224.50  
  Purchase #5 $158.63   4.669%   $166.0364   $166.04   $166.05   $166.00  
  Purchase #6 $78.44   12.417%   $88.1799   $88.18   $88.20   $88.20  
  Purchase #7 $100.81   8.639%   $109.519   $109.52   $109.50   $109.50  
  7 purchase totals = $1,019.97       $1,101.7560   $1,101.75   $1,101.80   $1,101.70