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 $206.60   12.782%   $233.0076   $233.01   $233.00   $233.00  
  Purchase #2 $81.48   4.206%   $84.907   $84.91   $84.90   $84.90  
  Purchase #3 $98.25   7.462%   $105.5814   $105.58   $105.60   $105.60  
  Purchase #4 $127.40   3.853%   $132.3087   $132.31   $132.30   $132.30  
  Purchase #5 $161.53   3.628%   $167.3903   $167.39   $167.40   $167.40  
  Purchase #6 $48.74   10.796%   $54.002   $54.00   $54.00   $54.00  
  Purchase #7 $5.47   9.761%   $6.0039   $6.00   $6.00   $6.00  
  7 purchase totals = $729.47       $783.2009   $783.20   $783.20   $783.20