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 $229.25   10.243%   $252.7321   $252.73   $252.75   $252.70  
  Purchase #2 $51.65   4.534%   $53.9918   $53.99   $54.00   $54.00  
  Purchase #3 $240.66   3.608%   $249.343   $249.34   $249.35   $249.30  
  Purchase #4 $149.46   6.505%   $159.1824   $159.18   $159.20   $159.20  
  Purchase #5 $46.44   11.412%   $51.7397   $51.74   $51.75   $51.70  
  Purchase #6 $240.98   11.699%   $269.1723   $269.17   $269.15   $269.20  
  Purchase #7 $218.38   4.134%   $227.4078   $227.41   $227.40   $227.40  
  7 purchase totals = $1,176.82       $1,263.5691   $1,263.56   $1,263.60   $1,263.50