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	$86.32	3.105%	$89.0002	$89.00	$89.00	$89.00
Purchase #2	$20.29	10.368%	$22.3937	$22.39	$22.40	$22.40
Purchase #3	$77.72	7.413%	$83.4814	$83.48	$83.50	$83.50
Purchase #4	$115.86	7.411%	$124.4464	$124.45	$124.45	$124.40
Purchase #5	$231.46	4.807%	$242.5863	$242.59	$242.60	$242.60
Purchase #6	$63.54	6.449%	$67.6377	$67.64	$67.65	$67.60
Purchase #7	$14.76	12.859%	$16.658	$16.66	$16.65	$16.70
7 purchase totals =	$609.95		$646.2037	$646.21	$646.25	$646.20