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 $20.69   3.447%   $21.4032   $21.40   $21.40   $21.40  
  Purchase #2 $34.59   3.595%   $35.8335   $35.83   $35.85   $35.80  
  Purchase #3 $32.82   6.588%   $34.9822   $34.98   $35.00   $35.00  
  Purchase #4 $159.56   7.733%   $171.8988   $171.90   $171.90   $171.90  
  Purchase #5 $227.79   4.278%   $237.5349   $237.53   $237.55   $237.50  
  Purchase #6 $144.94   12.680%   $163.3184   $163.32   $163.30   $163.30  
  Purchase #7 $48.73   7.457%   $52.3638   $52.36   $52.35   $52.40  
  7 purchase totals = $669.12       $717.3348   $717.32   $717.35   $717.30