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 $45.94   5.413%   $48.4267   $48.43   $48.45   $48.40  
  Purchase #2 $110.31   8.569%   $119.7625   $119.76   $119.75   $119.80  
  Purchase #3 $221.88   4.719%   $232.3505   $232.35   $232.35   $232.40  
  Purchase #4 $198.64   9.654%   $217.8167   $217.82   $217.80   $217.80  
  Purchase #5 $83.28   11.198%   $92.6057   $92.61   $92.60   $92.60  
  Purchase #6 $208.72   8.592%   $226.6532   $226.65   $226.65   $226.70  
  Purchase #7 $55.63   8.388%   $60.2962   $60.30   $60.30   $60.30  
  7 purchase totals = $924.40       $997.9115   $997.92   $997.90   $998.00