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 $227.92   7.727%   $245.5314   $245.53   $245.55   $245.50  
  Purchase #2 $205.75   12.530%   $231.5305   $231.53   $231.55   $231.50  
  Purchase #3 $60.90   8.376%   $66.001   $66.00   $66.00   $66.00  
  Purchase #4 $66.82   8.685%   $72.6233   $72.62   $72.60   $72.60  
  Purchase #5 $5.93   7.104%   $6.3513   $6.35   $6.35   $6.40  
  Purchase #6 $151.90   8.471%   $164.7674   $164.77   $164.75   $164.80  
  Purchase #7 $25.93   5.818%   $27.4386   $27.44   $27.45   $27.40  
  7 purchase totals = $745.15       $814.2435   $814.24   $814.25   $814.20