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 $92.30   6.544%   $98.3401   $98.34   $98.35   $98.30  
  Purchase #2 $57.97   3.839%   $60.1955   $60.20   $60.20   $60.20  
  Purchase #3 $32.98   8.109%   $35.6543   $35.65   $35.65   $35.70  
  Purchase #4 $101.62   11.125%   $112.9252   $112.93   $112.95   $112.90  
  Purchase #5 $126.40   12.718%   $142.4756   $142.48   $142.50   $142.50  
  Purchase #6 $216.83   9.235%   $236.8543   $236.85   $236.85   $236.90  
  Purchase #7 $124.94   4.322%   $130.3399   $130.34   $130.35   $130.30  
  7 purchase totals = $753.04       $816.7849   $816.79   $816.85   $816.80