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 $84.44   12.340%   $94.8599   $94.86   $94.85   $94.90  
  Purchase #2 $146.92   3.786%   $152.4824   $152.48   $152.50   $152.50  
  Purchase #3 $106.54   7.836%   $114.8885   $114.89   $114.90   $114.90  
  Purchase #4 $72.46   7.282%   $77.7365   $77.74   $77.75   $77.70  
  Purchase #5 $84.39   12.507%   $94.9447   $94.94   $94.95   $94.90  
  Purchase #6 $206.77   7.422%   $222.1165   $222.12   $222.10   $222.10  
  Purchase #7 $232.94   3.468%   $241.0184   $241.02   $241.00   $241.00  
  7 purchase totals = $934.46       $998.0469   $998.05   $998.05   $998.00