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	$105.27	5.582%	$111.1462	$111.15	$111.15	$111.10
Purchase #2	$78.86	3.605%	$81.7029	$81.70	$81.70	$81.70
Purchase #3	$228.36	6.608%	$243.45	$243.45	$243.45	$243.50
Purchase #4	$144.32	13.823%	$164.2694	$164.27	$164.25	$164.30
Purchase #5	$80.74	6.379%	$85.8904	$85.89	$85.90	$85.90
Purchase #6	$22.26	7.571%	$23.9453	$23.95	$23.95	$23.90
Purchase #7	$114.64	13.573%	$130.2001	$130.20	$130.20	$130.20
7 purchase totals =	$774.45		$840.6043	$840.61	$840.60	$840.60