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 $24.31   4.731%   $25.4601   $25.46   $25.45   $25.50  
  Purchase #2 $217.55   12.296%   $244.2999   $244.30   $244.30   $244.30  
  Purchase #3 $174.76   4.230%   $182.1523   $182.15   $182.15   $182.20  
  Purchase #4 $73.78   12.336%   $82.8815   $82.88   $82.90   $82.90  
  Purchase #5 $157.92   13.609%   $179.4113   $179.41   $179.40   $179.40  
  Purchase #6 $16.94   5.472%   $17.867   $17.87   $17.85   $17.90  
  Purchase #7 $34.56   6.354%   $36.7559   $36.76   $36.75   $36.80  
  7 purchase totals = $699.82       $768.8280   $768.83   $768.80   $769.00