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 $212.71   11.792%   $237.7928   $237.79   $237.80   $237.80  
  Purchase #2 $192.57   11.124%   $213.9915   $213.99   $214.00   $214.00  
  Purchase #3 $86.64   7.242%   $92.9145   $92.91   $92.90   $92.90  
  Purchase #4 $229.50   9.145%   $250.4878   $250.49   $250.50   $250.50  
  Purchase #5 $221.44   4.844%   $232.1666   $232.17   $232.15   $232.20  
  Purchase #6 $117.99   6.725%   $125.9248   $125.92   $125.90   $125.90  
  Purchase #7 $107.30   4.682%   $112.3238   $112.32   $112.30   $112.30  
  7 purchase totals = $1,168.15       $1,265.6018   $1,265.59   $1,265.55   $1,265.60