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 $23.59   10.205%   $25.9974   $26.00   $26.00   $26.00  
  Purchase #2 $74.60   11.224%   $82.9731   $82.97   $82.95   $83.00  
  Purchase #3 $226.46   10.393%   $249.996   $250.00   $250.00   $250.00  
  Purchase #4 $128.82   6.709%   $137.4625   $137.46   $137.45   $137.50  
  Purchase #5 $182.54   7.123%   $195.5423   $195.54   $195.55   $195.50  
  Purchase #6 $186.95   11.857%   $209.1167   $209.12   $209.10   $209.10  
  Purchase #7 $27.84   13.297%   $31.5419   $31.54   $31.55   $31.50  
  7 purchase totals = $850.80       $932.6299   $932.63   $932.60   $932.60