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 $154.96   5.773%   $163.9058   $163.91   $163.90   $163.90  
  Purchase #2 $240.76   10.247%   $265.4307   $265.43   $265.45   $265.40  
  Purchase #3 $46.26   12.614%   $52.0952   $52.10   $52.10   $52.10  
  Purchase #4 $220.63   12.846%   $248.9721   $248.97   $248.95   $249.00  
  Purchase #5 $116.62   11.823%   $130.408   $130.41   $130.40   $130.40  
  Purchase #6 $116.63   12.601%   $131.3265   $131.33   $131.35   $131.30  
  Purchase #7 $231.64   4.785%   $242.724   $242.72   $242.70   $242.70  
  7 purchase totals = $1,127.50       $1,234.8623   $1,234.87   $1,234.85   $1,234.80