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	$121.34	11.105%	$134.8148	$134.81	$134.80	$134.80
Purchase #2	$114.63	9.706%	$125.756	$125.76	$125.75	$125.80
Purchase #3	$81.81	10.479%	$90.3829	$90.38	$90.40	$90.40
Purchase #4	$14.89	7.159%	$15.956	$15.96	$15.95	$16.00
Purchase #5	$220.69	5.387%	$232.5786	$232.58	$232.60	$232.60
Purchase #6	$169.68	5.850%	$179.6063	$179.61	$179.60	$179.60
Purchase #7	$53.38	11.460%	$59.4973	$59.50	$59.50	$59.50
7 purchase totals =	$776.42		$838.5919	$838.60	$838.60	$838.70