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 $22.88   10.148%   $25.2019   $25.20   $25.20   $25.20  
  Purchase #2 $158.86   5.509%   $167.6116   $167.61   $167.60   $167.60  
  Purchase #3 $249.90   4.288%   $260.6157   $260.62   $260.60   $260.60  
  Purchase #4 $164.42   11.489%   $183.3102   $183.31   $183.30   $183.30  
  Purchase #5 $24.70   6.507%   $26.3072   $26.31   $26.30   $26.30  
  Purchase #6 $15.53   7.809%   $16.7427   $16.74   $16.75   $16.70  
  Purchase #7 $250.94   12.323%   $281.8633   $281.86   $281.85   $281.90  
  7 purchase totals = $887.23       $961.6526   $961.65   $961.60   $961.60