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 $239.33   6.860%   $255.748   $255.75   $255.75   $255.70  
  Purchase #2 $147.65   3.116%   $152.2508   $152.25   $152.25   $152.30  
  Purchase #3 $244.54   6.688%   $260.8948   $260.89   $260.90   $260.90  
  Purchase #4 $21.45   11.806%   $23.9824   $23.98   $24.00   $24.00  
  Purchase #5 $214.97   5.363%   $226.4988   $226.50   $226.50   $226.50  
  Purchase #6 $141.99   10.787%   $157.3065   $157.31   $157.30   $157.30  
  Purchase #7 $166.72   7.669%   $179.5058   $179.51   $179.50   $179.50  
  7 purchase totals = $1,176.65       $1,256.1871   $1,256.19   $1,256.20   $1,256.20