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	$9.67	7.253%	$10.3714	$10.37	$10.35	$10.40
Purchase #2	$50.78	4.249%	$52.9376	$52.94	$52.95	$52.90
Purchase #3	$5.45	5.129%	$5.7295	$5.73	$5.75	$5.70
Purchase #4	$70.37	3.227%	$72.6408	$72.64	$72.65	$72.60
Purchase #5	$230.62	8.521%	$250.2711	$250.27	$250.25	$250.30
Purchase #6	$250.52	5.744%	$264.9099	$264.91	$264.90	$264.90
Purchase #7	$32.29	9.358%	$35.3117	$35.31	$35.30	$35.30
7 purchase totals =	$649.70		$692.1720	$692.17	$692.15	$692.10