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 $61.50   10.723%   $68.0946   $68.09   $68.10   $68.10  
  Purchase #2 $107.65   3.710%   $111.6438   $111.64   $111.65   $111.60  
  Purchase #3 $216.87   3.122%   $223.6407   $223.64   $223.65   $223.60  
  Purchase #4 $94.83   8.685%   $103.066   $103.07   $103.05   $103.10  
  Purchase #5 $188.34   9.483%   $206.2003   $206.20   $206.20   $206.20  
  Purchase #6 $132.42   6.765%   $141.3782   $141.38   $141.40   $141.40  
  Purchase #7 $44.86   11.245%   $49.9045   $49.90   $49.90   $49.90  
  7 purchase totals = $846.47       $903.9281   $903.92   $903.95   $903.90