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 $32.28   3.674%   $33.466   $33.47   $33.45   $33.50  
  Purchase #2 $210.64   5.281%   $221.7639   $221.76   $221.75   $221.80  
  Purchase #3 $44.69   4.435%   $46.672   $46.67   $46.65   $46.70  
  Purchase #4 $210.31   12.269%   $236.1129   $236.11   $236.10   $236.10  
  Purchase #5 $187.65   4.377%   $195.8634   $195.86   $195.85   $195.90  
  Purchase #6 $162.90   3.145%   $168.0232   $168.02   $168.00   $168.00  
  Purchase #7 $130.75   4.780%   $136.9999   $137.00   $137.00   $137.00  
  7 purchase totals = $979.22       $1,038.9013   $1,038.89   $1,038.80   $1,039.00