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 $53.32   8.378%   $57.7871   $57.79   $57.80   $57.80  
  Purchase #2 $123.98   13.443%   $140.6466   $140.65   $140.65   $140.60  
  Purchase #3 $25.94   11.451%   $28.9104   $28.91   $28.90   $28.90  
  Purchase #4 $234.48   5.856%   $248.2111   $248.21   $248.20   $248.20  
  Purchase #5 $189.95   5.129%   $199.6925   $199.69   $199.70   $199.70  
  Purchase #6 $98.89   13.199%   $111.9425   $111.94   $111.95   $111.90  
  Purchase #7 $160.70   5.272%   $169.1721   $169.17   $169.15   $169.20  
  7 purchase totals = $887.26       $956.3623   $956.36   $956.35   $956.30