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 $208.59   13.564%   $236.8831   $236.88   $236.90   $236.90  
  Purchase #2 $31.65   13.758%   $36.0044   $36.00   $36.00   $36.00  
  Purchase #3 $64.26   9.667%   $70.472   $70.47   $70.45   $70.50  
  Purchase #4 $162.40   3.728%   $168.4543   $168.45   $168.45   $168.50  
  Purchase #5 $248.65   8.319%   $269.3352   $269.34   $269.35   $269.30  
  Purchase #6 $109.74   7.670%   $118.1571   $118.16   $118.15   $118.20  
  Purchase #7 $155.49   6.674%   $165.8674   $165.87   $165.85   $165.90  
  7 purchase totals = $980.78       $1,065.1735   $1,065.17   $1,065.15   $1,065.30