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 $61.86   8.802%   $67.3049   $67.30   $67.30   $67.30  
  Purchase #2 $31.89   10.493%   $35.2362   $35.24   $35.25   $35.20  
  Purchase #3 $246.48   10.587%   $272.5748   $272.57   $272.55   $272.60  
  Purchase #4 $10.34   3.185%   $10.6693   $10.67   $10.65   $10.70  
  Purchase #5 $250.74   11.458%   $279.4698   $279.47   $279.45   $279.50  
  Purchase #6 $15.73   3.622%   $16.2997   $16.30   $16.30   $16.30  
  Purchase #7 $195.91   11.593%   $218.6218   $218.62   $218.60   $218.60  
  7 purchase totals = $812.95       $900.1765   $900.17   $900.10   $900.20