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 $33.73   6.366%   $35.8773   $35.88   $35.90   $35.90  
  Purchase #2 $185.87   6.761%   $198.4367   $198.44   $198.45   $198.40  
  Purchase #3 $161.95   4.558%   $169.3317   $169.33   $169.35   $169.30  
  Purchase #4 $125.92   5.776%   $133.1931   $133.19   $133.20   $133.20  
  Purchase #5 $217.28   4.533%   $227.1293   $227.13   $227.15   $227.10  
  Purchase #6 $187.97   10.798%   $208.267   $208.27   $208.25   $208.30  
  Purchase #7 $20.26   10.815%   $22.4511   $22.45   $22.45   $22.50  
  7 purchase totals = $932.98       $994.6862   $994.69   $994.75   $994.70