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	$27.45	3.581%	$28.433	$28.43	$28.45	$28.40
Purchase #2	$87.87	13.562%	$99.7869	$99.79	$99.80	$99.80
Purchase #3	$166.77	4.318%	$173.9711	$173.97	$173.95	$174.00
Purchase #4	$9.66	4.809%	$10.1245	$10.12	$10.10	$10.10
Purchase #5	$116.77	5.832%	$123.58	$123.58	$123.60	$123.60
Purchase #6	$213.55	11.692%	$238.5183	$238.52	$238.50	$238.50
Purchase #7	$222.98	13.871%	$253.9096	$253.91	$253.90	$253.90
7 purchase totals =	$845.05		$928.3234	$928.32	$928.30	$928.30