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 $108.38   8.190%   $117.2563   $117.26   $117.25   $117.30  
  Purchase #2 $108.75   4.739%   $113.9037   $113.90   $113.90   $113.90  
  Purchase #3 $90.81   4.598%   $94.9854   $94.99   $95.00   $95.00  
  Purchase #4 $99.88   7.501%   $107.372   $107.37   $107.35   $107.40  
  Purchase #5 $53.34   13.601%   $60.5948   $60.59   $60.60   $60.60  
  Purchase #6 $226.87   5.121%   $238.488   $238.49   $238.50   $238.50  
  Purchase #7 $193.36   4.396%   $201.8601   $201.86   $201.85   $201.90  
  7 purchase totals = $881.39       $934.4603   $934.46   $934.45   $934.60