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 $32.71   5.867%   $34.6291   $34.63   $34.65   $34.60  
  Purchase #2 $215.42   11.659%   $240.5358   $240.54   $240.55   $240.50  
  Purchase #3 $16.32   3.727%   $16.9282   $16.93   $16.95   $16.90  
  Purchase #4 $126.43   6.619%   $134.7984   $134.80   $134.80   $134.80  
  Purchase #5 $96.56   3.454%   $99.8952   $99.90   $99.90   $99.90  
  Purchase #6 $236.29   11.109%   $262.5395   $262.54   $262.55   $262.50  
  Purchase #7 $135.59   9.575%   $148.5727   $148.57   $148.55   $148.60  
  7 purchase totals = $859.32       $937.8989   $937.91   $937.95   $937.80