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 $92.78   12.127%   $104.0314   $104.03   $104.05   $104.00  
  Purchase #2 $76.64   10.143%   $84.4136   $84.41   $84.40   $84.40  
  Purchase #3 $30.36   10.496%   $33.5466   $33.55   $33.55   $33.50  
  Purchase #4 $81.26   7.563%   $87.4057   $87.41   $87.40   $87.40  
  Purchase #5 $92.86   10.824%   $102.9112   $102.91   $102.90   $102.90  
  Purchase #6 $152.76   10.634%   $169.0045   $169.00   $169.00   $169.00  
  Purchase #7 $203.60   8.776%   $221.4679   $221.47   $221.45   $221.50  
  7 purchase totals = $730.26       $802.7809   $802.78   $802.75   $802.70