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 $250.92   6.802%   $267.9876   $267.99   $268.00   $268.00  
  Purchase #2 $174.78   9.391%   $191.1936   $191.19   $191.20   $191.20  
  Purchase #3 $215.74   4.676%   $225.828   $225.83   $225.85   $225.80  
  Purchase #4 $193.55   8.796%   $210.5747   $210.57   $210.55   $210.60  
  Purchase #5 $226.27   4.804%   $237.14   $237.14   $237.15   $237.10  
  Purchase #6 $206.34   3.426%   $213.4092   $213.41   $213.40   $213.40  
  Purchase #7 $172.95   3.141%   $178.3824   $178.38   $178.40   $178.40  
  7 purchase totals = $1,440.55       $1,524.5155   $1,524.51   $1,524.55   $1,524.50