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 $241.95   7.474%   $260.0333   $260.03   $260.05   $260.00  
  Purchase #2 $13.81   5.135%   $14.5191   $14.52   $14.50   $14.50  
  Purchase #3 $6.34   11.159%   $7.0475   $7.05   $7.05   $7.00  
  Purchase #4 $141.62   12.731%   $159.6496   $159.65   $159.65   $159.60  
  Purchase #5 $106.35   10.817%   $117.8539   $117.85   $117.85   $117.90  
  Purchase #6 $125.81   8.599%   $136.6284   $136.63   $136.65   $136.60  
  Purchase #7 $237.26   6.675%   $253.0971   $253.10   $253.10   $253.10  
  7 purchase totals = $873.14       $948.8289   $948.83   $948.85   $948.70