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 $182.98   3.202%   $188.839   $188.84   $188.85   $188.80  
  Purchase #2 $74.88   5.177%   $78.7565   $78.76   $78.75   $78.80  
  Purchase #3 $244.82   13.838%   $278.6982   $278.70   $278.70   $278.70  
  Purchase #4 $163.53   8.479%   $177.3957   $177.40   $177.40   $177.40  
  Purchase #5 $38.55   12.236%   $43.267   $43.27   $43.25   $43.30  
  Purchase #6 $126.61   11.266%   $140.8739   $140.87   $140.85   $140.90  
  Purchase #7 $106.55   9.333%   $116.4943   $116.49   $116.50   $116.50  
  7 purchase totals = $937.92       $1,024.3246   $1,024.33   $1,024.30   $1,024.40