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 $109.68   8.627%   $119.1421   $119.14   $119.15   $119.10  
  Purchase #2 $53.66   13.497%   $60.9025   $60.90   $60.90   $60.90  
  Purchase #3 $231.54   12.851%   $261.2952   $261.30   $261.30   $261.30  
  Purchase #4 $31.51   4.431%   $32.9062   $32.91   $32.90   $32.90  
  Purchase #5 $101.71   7.839%   $109.683   $109.68   $109.70   $109.70  
  Purchase #6 $157.57   4.687%   $164.9553   $164.96   $164.95   $165.00  
  Purchase #7 $248.75   11.599%   $277.6025   $277.60   $277.60   $277.60  
  7 purchase totals = $934.42       $1,026.4868   $1,026.49   $1,026.50   $1,026.50