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 $201.32   3.332%   $208.028   $208.03   $208.05   $208.00  
  Purchase #2 $35.78   8.372%   $38.7755   $38.78   $38.80   $38.80  
  Purchase #3 $21.92   11.664%   $24.4767   $24.48   $24.50   $24.50  
  Purchase #4 $125.26   3.456%   $129.589   $129.59   $129.60   $129.60  
  Purchase #5 $78.34   8.769%   $85.2096   $85.21   $85.20   $85.20  
  Purchase #6 $13.90   9.732%   $15.2527   $15.25   $15.25   $15.30  
  Purchase #7 $222.89   4.183%   $232.2135   $232.21   $232.20   $232.20  
  7 purchase totals = $699.41       $733.5450   $733.55   $733.60   $733.60