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	$221.72	7.408%	$238.145	$238.15	$238.15	$238.10
Purchase #2	$147.40	12.829%	$166.3099	$166.31	$166.30	$166.30
Purchase #3	$177.55	7.721%	$191.2586	$191.26	$191.25	$191.30
Purchase #4	$97.44	7.846%	$105.0851	$105.09	$105.10	$105.10
Purchase #5	$85.50	5.834%	$90.4881	$90.49	$90.50	$90.50
Purchase #6	$95.43	7.668%	$102.7476	$102.75	$102.75	$102.70
Purchase #7	$17.78	13.548%	$20.1888	$20.19	$20.20	$20.20
7 purchase totals =	$842.82		$914.2231	$914.24	$914.25	$914.20