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 $236.26   4.271%   $246.3507   $246.35   $246.35   $246.40  
  Purchase #2 $210.44   5.616%   $222.2583   $222.26   $222.25   $222.30  
  Purchase #3 $78.73   7.401%   $84.5568   $84.56   $84.55   $84.60  
  Purchase #4 $18.31   5.190%   $19.2603   $19.26   $19.25   $19.30  
  Purchase #5 $81.80   7.606%   $88.0217   $88.02   $88.00   $88.00  
  Purchase #6 $183.87   5.283%   $193.5839   $193.58   $193.60   $193.60  
  Purchase #7 $92.42   5.128%   $97.1593   $97.16   $97.15   $97.20  
  7 purchase totals = $901.83       $951.1910   $951.19   $951.15   $951.40