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	$38.54	4.587%	$40.3078	$40.31	$40.30	$40.30
Purchase #2	$154.45	4.783%	$161.8373	$161.84	$161.85	$161.80
Purchase #3	$93.87	6.801%	$100.2541	$100.25	$100.25	$100.30
Purchase #4	$132.65	8.318%	$143.6838	$143.68	$143.70	$143.70
Purchase #5	$228.70	8.302%	$247.6867	$247.69	$247.70	$247.70
Purchase #6	$134.57	12.418%	$151.2809	$151.28	$151.30	$151.30
Purchase #7	$40.68	3.608%	$42.1477	$42.15	$42.15	$42.10
7 purchase totals =	$823.46		$887.1983	$887.20	$887.25	$887.20