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 $227.87   9.420%   $249.3354   $249.34   $249.35   $249.30  
  Purchase #2 $194.50   11.496%   $216.8597   $216.86   $216.85   $216.90  
  Purchase #3 $110.67   11.711%   $123.6306   $123.63   $123.65   $123.60  
  Purchase #4 $213.66   9.775%   $234.5453   $234.55   $234.55   $234.50  
  Purchase #5 $109.98   4.451%   $114.8752   $114.88   $114.90   $114.90  
  Purchase #6 $231.45   9.674%   $253.8405   $253.84   $253.85   $253.80  
  Purchase #7 $166.72   5.667%   $176.168   $176.17   $176.15   $176.20  
  7 purchase totals = $1,254.85       $1,369.2547   $1,369.27   $1,369.30   $1,369.20