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	$88.29	11.501%	$98.4442	$98.44	$98.45	$98.40
Purchase #2	$147.67	3.249%	$152.4678	$152.47	$152.45	$152.50
Purchase #3	$181.30	11.551%	$202.242	$202.24	$202.25	$202.20
Purchase #4	$30.88	6.672%	$32.9403	$32.94	$32.95	$32.90
Purchase #5	$82.40	11.285%	$91.6988	$91.70	$91.70	$91.70
Purchase #6	$101.67	9.240%	$111.0643	$111.06	$111.05	$111.10
Purchase #7	$136.64	11.185%	$151.9232	$151.92	$151.90	$151.90
7 purchase totals =	$768.85		$840.7806	$840.77	$840.75	$840.70