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 $25.76   3.502%   $26.6621   $26.66   $26.65   $26.70  
  Purchase #2 $177.36   9.543%   $194.2855   $194.29   $194.30   $194.30  
  Purchase #3 $246.79   12.731%   $278.2088   $278.21   $278.20   $278.20  
  Purchase #4 $241.65   8.379%   $261.8979   $261.90   $261.90   $261.90  
  Purchase #5 $215.60   6.241%   $229.0556   $229.06   $229.05   $229.10  
  Purchase #6 $34.50   5.449%   $36.3799   $36.38   $36.40   $36.40  
  Purchase #7 $14.33   4.567%   $14.9845   $14.98   $15.00   $15.00  
  7 purchase totals = $955.99       $1,041.4743   $1,041.48   $1,041.50   $1,041.60