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 $211.26   13.433%   $239.6386   $239.64   $239.65   $239.60  
  Purchase #2 $94.95   10.253%   $104.6852   $104.69   $104.70   $104.70  
  Purchase #3 $16.96   13.695%   $19.2827   $19.28   $19.30   $19.30  
  Purchase #4 $150.69   12.573%   $169.6363   $169.64   $169.65   $169.60  
  Purchase #5 $236.38   12.796%   $266.6272   $266.63   $266.65   $266.60  
  Purchase #6 $66.59   6.491%   $70.9124   $70.91   $70.90   $70.90  
  Purchase #7 $29.60   4.200%   $30.8432   $30.84   $30.85   $30.80  
  7 purchase totals = $806.43       $901.6256   $901.63   $901.70   $901.50