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	$25.45	12.398%	$28.6053	$28.61	$28.60	$28.60
Purchase #2	$44.97	7.688%	$48.4273	$48.43	$48.45	$48.40
Purchase #3	$81.69	5.388%	$86.0915	$86.09	$86.10	$86.10
Purchase #4	$195.65	12.309%	$219.7326	$219.73	$219.75	$219.70
Purchase #5	$37.83	12.196%	$42.4437	$42.44	$42.45	$42.40
Purchase #6	$200.56	11.167%	$222.9565	$222.96	$222.95	$223.00
Purchase #7	$219.35	3.521%	$227.0733	$227.07	$227.05	$227.10
7 purchase totals =	$805.50		$875.3302	$875.33	$875.35	$875.30