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 $94.74   3.789%   $98.3297   $98.33   $98.35   $98.30  
  Purchase #2 $9.95   12.293%   $11.1732   $11.17   $11.15   $11.20  
  Purchase #3 $202.27   13.477%   $229.5299   $229.53   $229.55   $229.50  
  Purchase #4 $125.26   8.853%   $136.3493   $136.35   $136.35   $136.30  
  Purchase #5 $161.69   4.551%   $169.0485   $169.05   $169.05   $169.00  
  Purchase #6 $213.41   9.641%   $233.9849   $233.98   $234.00   $234.00  
  Purchase #7 $236.72   10.498%   $261.5709   $261.57   $261.55   $261.60  
  7 purchase totals = $1,044.04       $1,139.9864   $1,139.98   $1,140.00   $1,139.90