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 $114.82   3.423%   $118.7503   $118.75   $118.75   $118.80  
  Purchase #2 $232.73   10.394%   $256.92   $256.92   $256.90   $256.90  
  Purchase #3 $169.37   7.759%   $182.5114   $182.51   $182.50   $182.50  
  Purchase #4 $35.60   11.396%   $39.657   $39.66   $39.65   $39.70  
  Purchase #5 $22.70   4.542%   $23.731   $23.73   $23.75   $23.70  
  Purchase #6 $134.96   4.287%   $140.7457   $140.75   $140.75   $140.70  
  Purchase #7 $78.73   6.467%   $83.8215   $83.82   $83.80   $83.80  
  7 purchase totals = $788.91       $846.1369   $846.14   $846.10   $846.10