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 $212.68   12.611%   $239.5011   $239.50   $239.50   $239.50  
  Purchase #2 $112.62   3.736%   $116.8275   $116.83   $116.85   $116.80  
  Purchase #3 $79.40   9.424%   $86.8827   $86.88   $86.90   $86.90  
  Purchase #4 $108.77   7.485%   $116.9114   $116.91   $116.90   $116.90  
  Purchase #5 $118.62   11.316%   $132.043   $132.04   $132.05   $132.00  
  Purchase #6 $97.76   10.651%   $108.1724   $108.17   $108.15   $108.20  
  Purchase #7 $190.25   12.442%   $213.9209   $213.92   $213.90   $213.90  
  7 purchase totals = $920.10       $1,014.2590   $1,014.25   $1,014.25   $1,014.20