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 $58.44   4.790%   $61.2393   $61.24   $61.25   $61.20  
  Purchase #2 $223.63   5.741%   $236.4686   $236.47   $236.45   $236.50  
  Purchase #3 $195.97   5.166%   $206.0938   $206.09   $206.10   $206.10  
  Purchase #4 $36.41   5.205%   $38.3051   $38.31   $38.30   $38.30  
  Purchase #5 $15.43   9.610%   $16.9128   $16.91   $16.90   $16.90  
  Purchase #6 $227.90   10.836%   $252.5952   $252.60   $252.60   $252.60  
  Purchase #7 $33.42   7.596%   $35.9586   $35.96   $35.95   $36.00  
  7 purchase totals = $791.20       $847.5734   $847.58   $847.55   $847.60