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	$74.97	4.622%	$78.4351	$78.44	$78.45	$78.40
Purchase #2	$88.51	12.857%	$99.8897	$99.89	$99.90	$99.90
Purchase #3	$37.62	7.350%	$40.3851	$40.39	$40.40	$40.40
Purchase #4	$48.61	12.369%	$54.6226	$54.62	$54.60	$54.60
Purchase #5	$102.77	7.694%	$110.6771	$110.68	$110.70	$110.70
Purchase #6	$192.70	11.183%	$214.2496	$214.25	$214.25	$214.20
Purchase #7	$190.47	6.123%	$202.1325	$202.13	$202.15	$202.10
7 purchase totals =	$735.65		$800.3917	$800.40	$800.45	$800.30