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 $41.83   6.465%   $44.5343   $44.53   $44.55   $44.50  
  Purchase #2 $14.91   6.412%   $15.866   $15.87   $15.85   $15.90  
  Purchase #3 $238.68   10.139%   $262.8798   $262.88   $262.90   $262.90  
  Purchase #4 $149.26   3.842%   $154.9946   $154.99   $155.00   $155.00  
  Purchase #5 $138.90   10.507%   $153.4942   $153.49   $153.50   $153.50  
  Purchase #6 $238.35   4.162%   $248.2701   $248.27   $248.25   $248.30  
  Purchase #7 $194.49   13.808%   $221.3452   $221.35   $221.35   $221.30  
  7 purchase totals = $1,016.42       $1,101.3842   $1,101.38   $1,101.40   $1,101.40