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 $126.67   11.554%   $141.3055   $141.31   $141.30   $141.30  
  Purchase #2 $25.99   11.438%   $28.9627   $28.96   $28.95   $29.00  
  Purchase #3 $55.77   7.574%   $59.994   $59.99   $60.00   $60.00  
  Purchase #4 $46.61   11.269%   $51.8625   $51.86   $51.85   $51.90  
  Purchase #5 $210.69   5.707%   $222.7141   $222.71   $222.70   $222.70  
  Purchase #6 $6.90   8.446%   $7.4828   $7.48   $7.50   $7.50  
  Purchase #7 $240.63   6.774%   $256.9303   $256.93   $256.95   $256.90  
  7 purchase totals = $713.26       $769.2519   $769.24   $769.25   $769.30