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 $51.33   10.361%   $56.6483   $56.65   $56.65   $56.60  
  Purchase #2 $27.47   7.806%   $29.6143   $29.61   $29.60   $29.60  
  Purchase #3 $236.94   4.318%   $247.1711   $247.17   $247.15   $247.20  
  Purchase #4 $72.50   7.103%   $77.6497   $77.65   $77.65   $77.60  
  Purchase #5 $230.53   10.431%   $254.5766   $254.58   $254.60   $254.60  
  Purchase #6 $22.67   9.230%   $24.7624   $24.76   $24.75   $24.80  
  Purchase #7 $114.83   3.816%   $119.2119   $119.21   $119.20   $119.20  
  7 purchase totals = $756.27       $809.6343   $809.63   $809.60   $809.60