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 $23.57   10.390%   $26.0189   $26.02   $26.00   $26.00  
  Purchase #2 $20.66   13.306%   $23.409   $23.41   $23.40   $23.40  
  Purchase #3 $19.36   12.384%   $21.7575   $21.76   $21.75   $21.80  
  Purchase #4 $146.43   12.756%   $165.1086   $165.11   $165.10   $165.10  
  Purchase #5 $162.56   13.661%   $184.7673   $184.77   $184.75   $184.80  
  Purchase #6 $5.68   13.447%   $6.4438   $6.44   $6.45   $6.40  
  Purchase #7 $112.27   9.829%   $123.305   $123.31   $123.30   $123.30  
  7 purchase totals = $490.53       $550.8101   $550.82   $550.75   $550.80