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 $193.41   11.613%   $215.8707   $215.87   $215.85   $215.90  
  Purchase #2 $140.86   3.386%   $145.6295   $145.63   $145.65   $145.60  
  Purchase #3 $63.97   4.516%   $66.8589   $66.86   $66.85   $66.90  
  Purchase #4 $143.75   13.324%   $162.9033   $162.90   $162.90   $162.90  
  Purchase #5 $11.33   12.701%   $12.769   $12.77   $12.75   $12.80  
  Purchase #6 $217.97   4.399%   $227.5585   $227.56   $227.55   $227.60  
  Purchase #7 $187.86   13.188%   $212.635   $212.64   $212.65   $212.60  
  7 purchase totals = $959.15       $1,044.2249   $1,044.23   $1,044.20   $1,044.30