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 $141.25   9.193%   $154.2351   $154.24   $154.25   $154.20  
  Purchase #2 $108.30   10.185%   $119.3304   $119.33   $119.35   $119.30  
  Purchase #3 $202.47   4.159%   $210.8907   $210.89   $210.90   $210.90  
  Purchase #4 $16.40   10.749%   $18.1628   $18.16   $18.15   $18.20  
  Purchase #5 $75.95   13.368%   $86.103   $86.10   $86.10   $86.10  
  Purchase #6 $151.48   9.225%   $165.454   $165.45   $165.45   $165.50  
  Purchase #7 $31.45   9.277%   $34.3676   $34.37   $34.35   $34.40  
  7 purchase totals = $727.30       $788.5436   $788.54   $788.55   $788.60