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 $226.77   6.509%   $241.5305   $241.53   $241.55   $241.50  
  Purchase #2 $19.70   11.203%   $21.907   $21.91   $21.90   $21.90  
  Purchase #3 $16.54   4.543%   $17.2914   $17.29   $17.30   $17.30  
  Purchase #4 $21.61   9.632%   $23.6915   $23.69   $23.70   $23.70  
  Purchase #5 $167.96   6.419%   $178.7414   $178.74   $178.75   $178.70  
  Purchase #6 $179.76   6.308%   $191.0993   $191.10   $191.10   $191.10  
  Purchase #7 $198.84   7.389%   $213.5323   $213.53   $213.55   $213.50  
  7 purchase totals = $831.18       $887.7934   $887.79   $887.85   $887.70