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 $211.48   7.648%   $227.654   $227.65   $227.65   $227.70  
  Purchase #2 $45.61   5.847%   $48.2768   $48.28   $48.30   $48.30  
  Purchase #3 $17.64   5.809%   $18.6647   $18.66   $18.65   $18.70  
  Purchase #4 $146.76   11.412%   $163.5083   $163.51   $163.50   $163.50  
  Purchase #5 $105.78   5.331%   $111.4191   $111.42   $111.40   $111.40  
  Purchase #6 $72.76   5.189%   $76.5355   $76.54   $76.55   $76.50  
  Purchase #7 $8.67   6.146%   $9.2029   $9.20   $9.20   $9.20  
  7 purchase totals = $608.70       $655.2613   $655.26   $655.25   $655.30