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	$152.46	13.304%	$172.7433	$172.74	$172.75	$172.70
Purchase #2	$12.30	5.663%	$12.9965	$13.00	$13.00	$13.00
Purchase #3	$12.47	8.734%	$13.5591	$13.56	$13.55	$13.60
Purchase #4	$217.63	3.483%	$225.2101	$225.21	$225.20	$225.20
Purchase #5	$35.38	5.745%	$37.4126	$37.41	$37.40	$37.40
Purchase #6	$45.47	13.176%	$51.4611	$51.46	$51.45	$51.50
Purchase #7	$160.65	11.400%	$178.9641	$178.96	$178.95	$179.00
7 purchase totals =	$636.36		$692.3468	$692.34	$692.30	$692.40