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 $87.26   8.528%   $94.7015   $94.70   $94.70   $94.70  
  Purchase #2 $109.83   11.769%   $122.7559   $122.76   $122.75   $122.80  
  Purchase #3 $213.79   9.399%   $233.8841   $233.88   $233.90   $233.90  
  Purchase #4 $73.39   7.547%   $78.9287   $78.93   $78.95   $78.90  
  Purchase #5 $33.70   6.874%   $36.0165   $36.02   $36.00   $36.00  
  Purchase #6 $230.42   8.329%   $249.6117   $249.61   $249.60   $249.60  
  Purchase #7 $157.49   5.322%   $165.8716   $165.87   $165.85   $165.90  
  7 purchase totals = $905.88       $981.7700   $981.77   $981.75   $981.80