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	$227.55	4.727%	$238.3063	$238.31	$238.30	$238.30
Purchase #2	$62.77	11.584%	$70.0413	$70.04	$70.05	$70.00
Purchase #3	$121.89	9.847%	$133.8925	$133.89	$133.90	$133.90
Purchase #4	$136.70	7.247%	$146.6066	$146.61	$146.60	$146.60
Purchase #5	$110.31	3.699%	$114.3904	$114.39	$114.40	$114.40
Purchase #6	$154.29	12.385%	$173.3988	$173.40	$173.40	$173.40
Purchase #7	$206.64	7.504%	$222.1463	$222.15	$222.15	$222.10
7 purchase totals =	$1,020.15		$1,098.7822	$1,098.79	$1,098.80	$1,098.70