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 $69.57   6.126%   $73.8319   $73.83   $73.85   $73.80  
  Purchase #2 $125.54   6.277%   $133.4201   $133.42   $133.40   $133.40  
  Purchase #3 $248.72   6.664%   $265.2947   $265.29   $265.30   $265.30  
  Purchase #4 $64.37   8.107%   $69.5885   $69.59   $69.60   $69.60  
  Purchase #5 $131.30   6.731%   $140.1378   $140.14   $140.15   $140.10  
  Purchase #6 $219.58   3.495%   $227.2543   $227.25   $227.25   $227.30  
  Purchase #7 $217.99   7.674%   $234.7186   $234.72   $234.70   $234.70  
  7 purchase totals = $1,077.07       $1,144.2459   $1,144.24   $1,144.25   $1,144.20