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 $56.99   10.676%   $63.0743   $63.07   $63.05   $63.10  
  Purchase #2 $173.57   13.353%   $196.7468   $196.75   $196.75   $196.70  
  Purchase #3 $111.53   12.466%   $125.4333   $125.43   $125.45   $125.40  
  Purchase #4 $220.75   13.711%   $251.017   $251.02   $251.00   $251.00  
  Purchase #5 $135.34   7.586%   $145.6069   $145.61   $145.60   $145.60  
  Purchase #6 $145.26   12.326%   $163.1647   $163.16   $163.15   $163.20  
  Purchase #7 $114.58   3.426%   $118.5055   $118.51   $118.50   $118.50  
  7 purchase totals = $958.02       $1,063.5485   $1,063.55   $1,063.50   $1,063.50