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 $246.99   8.722%   $268.5325   $268.53   $268.55   $268.50  
  Purchase #2 $238.44   7.776%   $256.9811   $256.98   $257.00   $257.00  
  Purchase #3 $117.36   7.288%   $125.9132   $125.91   $125.90   $125.90  
  Purchase #4 $107.87   3.327%   $111.4588   $111.46   $111.45   $111.50  
  Purchase #5 $243.69   9.392%   $266.5774   $266.58   $266.60   $266.60  
  Purchase #6 $209.41   13.458%   $237.5924   $237.59   $237.60   $237.60  
  Purchase #7 $170.81   8.483%   $185.2998   $185.30   $185.30   $185.30  
  7 purchase totals = $1,334.57       $1,452.3552   $1,452.35   $1,452.40   $1,452.40