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	$177.62	4.333%	$185.3163	$185.32	$185.30	$185.30
Purchase #2	$101.92	9.202%	$111.2987	$111.30	$111.30	$111.30
Purchase #3	$42.67	11.564%	$47.6044	$47.60	$47.60	$47.60
Purchase #4	$124.44	8.362%	$134.8457	$134.85	$134.85	$134.80
Purchase #5	$131.55	4.696%	$137.7276	$137.73	$137.75	$137.70
Purchase #6	$138.65	6.382%	$147.4986	$147.50	$147.50	$147.50
Purchase #7	$53.56	10.467%	$59.1661	$59.17	$59.15	$59.20
7 purchase totals =	$770.41		$823.4574	$823.47	$823.45	$823.40