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 $92.49   11.579%   $103.1994   $103.20   $103.20   $103.20  
  Purchase #2 $236.96   10.448%   $261.7176   $261.72   $261.70   $261.70  
  Purchase #3 $235.42   8.129%   $254.5573   $254.56   $254.55   $254.60  
  Purchase #4 $51.51   4.376%   $53.7641   $53.76   $53.75   $53.80  
  Purchase #5 $101.62   11.413%   $113.2179   $113.22   $113.20   $113.20  
  Purchase #6 $240.27   5.187%   $252.7328   $252.73   $252.75   $252.70  
  Purchase #7 $29.67   9.527%   $32.4967   $32.50   $32.50   $32.50  
  7 purchase totals = $987.94       $1,071.6858   $1,071.69   $1,071.65   $1,071.70