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 $33.98   13.694%   $38.6332   $38.63   $38.65   $38.60  
  Purchase #2 $88.29   10.653%   $97.6955   $97.70   $97.70   $97.70  
  Purchase #3 $143.97   3.316%   $148.744   $148.74   $148.75   $148.70  
  Purchase #4 $57.97   13.390%   $65.7322   $65.73   $65.75   $65.70  
  Purchase #5 $117.25   9.115%   $127.9373   $127.94   $127.95   $127.90  
  Purchase #6 $153.45   5.231%   $161.477   $161.48   $161.50   $161.50  
  Purchase #7 $234.27   11.464%   $261.1267   $261.13   $261.15   $261.10  
  7 purchase totals = $829.18       $901.3459   $901.35   $901.45   $901.20