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 $200.51   8.141%   $216.8335   $216.83   $216.85   $216.80  
  Purchase #2 $224.26   10.464%   $247.7266   $247.73   $247.75   $247.70  
  Purchase #3 $218.64   9.397%   $239.1856   $239.19   $239.20   $239.20  
  Purchase #4 $243.76   7.461%   $261.9469   $261.95   $261.95   $261.90  
  Purchase #5 $47.64   8.205%   $51.5489   $51.55   $51.55   $51.50  
  Purchase #6 $26.88   10.254%   $29.6363   $29.64   $29.65   $29.60  
  Purchase #7 $186.90   11.364%   $208.1393   $208.14   $208.15   $208.10  
  7 purchase totals = $1,148.59       $1,255.0171   $1,255.03   $1,255.10   $1,254.80