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 $63.32   4.763%   $66.3359   $66.34   $66.35   $66.30  
  Purchase #2 $195.50   6.228%   $207.6757   $207.68   $207.70   $207.70  
  Purchase #3 $198.88   7.222%   $213.2431   $213.24   $213.25   $213.20  
  Purchase #4 $105.87   5.791%   $112.0009   $112.00   $112.00   $112.00  
  Purchase #5 $229.26   8.318%   $248.3298   $248.33   $248.35   $248.30  
  Purchase #6 $189.35   10.690%   $209.5915   $209.59   $209.60   $209.60  
  Purchase #7 $67.35   8.542%   $73.103   $73.10   $73.10   $73.10  
  7 purchase totals = $1,049.53       $1,130.2799   $1,130.28   $1,130.35   $1,130.20