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 $53.46   12.429%   $60.1045   $60.10   $60.10   $60.10  
  Purchase #2 $141.94   9.869%   $155.9481   $155.95   $155.95   $155.90  
  Purchase #3 $79.83   8.242%   $86.4096   $86.41   $86.40   $86.40  
  Purchase #4 $210.65   13.644%   $239.3911   $239.39   $239.40   $239.40  
  Purchase #5 $241.55   6.709%   $257.7556   $257.76   $257.75   $257.80  
  Purchase #6 $196.58   10.852%   $217.9129   $217.91   $217.90   $217.90  
  Purchase #7 $72.47   5.130%   $76.1877   $76.19   $76.20   $76.20  
  7 purchase totals = $996.48       $1,093.7095   $1,093.71   $1,093.70   $1,093.70