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 $206.83   3.698%   $214.4786   $214.48   $214.50   $214.50  
  Purchase #2 $239.38   12.273%   $268.7591   $268.76   $268.75   $268.80  
  Purchase #3 $229.45   6.793%   $245.0365   $245.04   $245.05   $245.00  
  Purchase #4 $34.41   4.568%   $35.9818   $35.98   $36.00   $36.00  
  Purchase #5 $245.73   5.685%   $259.6998   $259.70   $259.70   $259.70  
  Purchase #6 $221.48   12.238%   $248.5847   $248.58   $248.60   $248.60  
  Purchase #7 $129.59   13.741%   $147.397   $147.40   $147.40   $147.40  
  7 purchase totals = $1,306.87       $1,419.9375   $1,419.94   $1,420.00   $1,420.00