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 $250.55   11.454%   $279.248   $279.25   $279.25   $279.20  
  Purchase #2 $9.85   4.578%   $10.3009   $10.30   $10.30   $10.30  
  Purchase #3 $213.77   8.798%   $232.5775   $232.58   $232.60   $232.60  
  Purchase #4 $68.68   6.156%   $72.9079   $72.91   $72.90   $72.90  
  Purchase #5 $185.88   12.410%   $208.9477   $208.95   $208.95   $208.90  
  Purchase #6 $120.91   10.471%   $133.5705   $133.57   $133.55   $133.60  
  Purchase #7 $143.25   3.467%   $148.2165   $148.22   $148.20   $148.20  
  7 purchase totals = $992.89       $1,085.7690   $1,085.78   $1,085.75   $1,085.70