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 $210.42   10.277%   $232.0449   $232.04   $232.05   $232.00  
  Purchase #2 $229.97   11.182%   $255.6852   $255.69   $255.70   $255.70  
  Purchase #3 $117.30   10.367%   $129.4605   $129.46   $129.45   $129.50  
  Purchase #4 $69.74   13.175%   $78.9282   $78.93   $78.95   $78.90  
  Purchase #5 $54.80   11.495%   $61.0993   $61.10   $61.10   $61.10  
  Purchase #6 $25.41   6.644%   $27.0982   $27.10   $27.10   $27.10  
  Purchase #7 $66.40   13.167%   $75.1429   $75.14   $75.15   $75.10  
  7 purchase totals = $774.04       $859.4592   $859.46   $859.50   $859.40