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 $63.33   6.368%   $67.3629   $67.36   $67.35   $67.40  
  Purchase #2 $217.51   6.501%   $231.6503   $231.65   $231.65   $231.70  
  Purchase #3 $104.56   4.292%   $109.0477   $109.05   $109.05   $109.00  
  Purchase #4 $124.95   3.872%   $129.7881   $129.79   $129.80   $129.80  
  Purchase #5 $58.43   8.262%   $63.2575   $63.26   $63.25   $63.30  
  Purchase #6 $130.71   4.457%   $136.5357   $136.54   $136.55   $136.50  
  Purchase #7 $25.40   9.350%   $27.7749   $27.77   $27.75   $27.80  
  7 purchase totals = $724.89       $765.4171   $765.42   $765.40   $765.50