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 $235.51   12.731%   $265.4928   $265.49   $265.50   $265.50  
  Purchase #2 $53.85   12.579%   $60.6238   $60.62   $60.60   $60.60  
  Purchase #3 $118.36   8.262%   $128.1389   $128.14   $128.15   $128.10  
  Purchase #4 $166.34   11.742%   $185.8716   $185.87   $185.85   $185.90  
  Purchase #5 $62.69   4.285%   $65.3763   $65.38   $65.40   $65.40  
  Purchase #6 $175.36   7.194%   $187.9754   $187.98   $188.00   $188.00  
  Purchase #7 $11.99   10.430%   $13.2406   $13.24   $13.25   $13.20  
  7 purchase totals = $824.10       $906.7194   $906.72   $906.75   $906.70