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 $23.97   12.389%   $26.9396   $26.94   $26.95   $26.90  
  Purchase #2 $177.29   3.871%   $184.1529   $184.15   $184.15   $184.20  
  Purchase #3 $69.92   3.783%   $72.5651   $72.57   $72.55   $72.60  
  Purchase #4 $199.49   4.138%   $207.7449   $207.74   $207.75   $207.70  
  Purchase #5 $14.25   6.511%   $15.1778   $15.18   $15.20   $15.20  
  Purchase #6 $169.94   13.432%   $192.7663   $192.77   $192.75   $192.80  
  Purchase #7 $43.40   8.812%   $47.2244   $47.22   $47.20   $47.20  
  7 purchase totals = $698.26       $746.5710   $746.57   $746.55   $746.60