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 $142.85   10.605%   $157.9992   $158.00   $158.00   $158.00  
  Purchase #2 $195.53   8.561%   $212.2693   $212.27   $212.25   $212.30  
  Purchase #3 $24.50   7.117%   $26.2437   $26.24   $26.25   $26.20  
  Purchase #4 $241.33   13.335%   $273.5114   $273.51   $273.50   $273.50  
  Purchase #5 $9.99   5.174%   $10.5069   $10.51   $10.50   $10.50  
  Purchase #6 $25.27   3.159%   $26.0683   $26.07   $26.05   $26.10  
  Purchase #7 $127.85   9.137%   $139.5317   $139.53   $139.55   $139.50  
  7 purchase totals = $767.32       $846.1305   $846.13   $846.10   $846.10