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 $98.82   5.444%   $104.1998   $104.20   $104.20   $104.20  
  Purchase #2 $13.75   3.804%   $14.2731   $14.27   $14.25   $14.30  
  Purchase #3 $144.61   3.731%   $150.0054   $150.01   $150.00   $150.00  
  Purchase #4 $5.99   9.558%   $6.5625   $6.56   $6.55   $6.60  
  Purchase #5 $233.71   4.191%   $243.5048   $243.50   $243.50   $243.50  
  Purchase #6 $137.79   8.188%   $149.0722   $149.07   $149.05   $149.10  
  Purchase #7 $114.87   7.598%   $123.5978   $123.60   $123.60   $123.60  
  7 purchase totals = $749.54       $791.2156   $791.21   $791.15   $791.30