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 $196.81   8.854%   $214.2356   $214.24   $214.25   $214.20  
  Purchase #2 $14.96   12.734%   $16.865   $16.87   $16.85   $16.90  
  Purchase #3 $183.59   13.610%   $208.5766   $208.58   $208.60   $208.60  
  Purchase #4 $99.53   6.709%   $106.2075   $106.21   $106.20   $106.20  
  Purchase #5 $114.77   13.723%   $130.5199   $130.52   $130.50   $130.50  
  Purchase #6 $131.41   11.635%   $146.6996   $146.70   $146.70   $146.70  
  Purchase #7 $13.38   6.739%   $14.2817   $14.28   $14.30   $14.30  
  7 purchase totals = $754.45       $837.3859   $837.40   $837.40   $837.40