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 $229.65   7.462%   $246.7865   $246.79   $246.80   $246.80  
  Purchase #2 $119.39   10.559%   $131.9964   $132.00   $132.00   $132.00  
  Purchase #3 $199.96   4.575%   $209.1082   $209.11   $209.10   $209.10  
  Purchase #4 $48.81   4.195%   $50.8576   $50.86   $50.85   $50.90  
  Purchase #5 $58.32   4.537%   $60.966   $60.97   $60.95   $61.00  
  Purchase #6 $203.63   6.227%   $216.31   $216.31   $216.30   $216.30  
  Purchase #7 $222.94   11.868%   $249.3985   $249.40   $249.40   $249.40  
  7 purchase totals = $1,082.70       $1,165.4232   $1,165.44   $1,165.40   $1,165.50