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 $60.26   6.136%   $63.9576   $63.96   $63.95   $64.00  
  Purchase #2 $61.60   9.762%   $67.6134   $67.61   $67.60   $67.60  
  Purchase #3 $16.57   9.484%   $18.1415   $18.14   $18.15   $18.10  
  Purchase #4 $124.81   10.526%   $137.9475   $137.95   $137.95   $137.90  
  Purchase #5 $153.45   3.622%   $159.008   $159.01   $159.00   $159.00  
  Purchase #6 $240.49   13.368%   $272.6387   $272.64   $272.65   $272.60  
  Purchase #7 $20.56   6.808%   $21.9597   $21.96   $21.95   $22.00  
  7 purchase totals = $677.74       $741.2664   $741.27   $741.25   $741.20