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	$71.89	11.723%	$80.3177	$80.32	$80.30	$80.30
Purchase #2	$14.50	7.620%	$15.6049	$15.60	$15.60	$15.60
Purchase #3	$34.67	7.425%	$37.2442	$37.24	$37.25	$37.20
Purchase #4	$155.29	10.468%	$171.5458	$171.55	$171.55	$171.50
Purchase #5	$95.50	12.301%	$107.2475	$107.25	$107.25	$107.20
Purchase #6	$222.77	13.127%	$252.013	$252.01	$252.00	$252.00
Purchase #7	$55.50	11.247%	$61.7421	$61.74	$61.75	$61.70
7 purchase totals =	$650.12		$725.7152	$725.71	$725.70	$725.50