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 $249.47   8.312%   $270.2059   $270.21   $270.20   $270.20  
  Purchase #2 $80.66   13.779%   $91.7741   $91.77   $91.75   $91.80  
  Purchase #3 $51.36   13.681%   $58.3866   $58.39   $58.40   $58.40  
  Purchase #4 $167.81   4.495%   $175.3531   $175.35   $175.35   $175.40  
  Purchase #5 $13.97   8.179%   $15.1126   $15.11   $15.10   $15.10  
  Purchase #6 $239.72   9.351%   $262.1362   $262.14   $262.15   $262.10  
  Purchase #7 $152.47   10.383%   $168.301   $168.30   $168.30   $168.30  
  7 purchase totals = $955.46       $1,041.2695   $1,041.27   $1,041.25   $1,041.30