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	$169.79	9.284%	$185.5533	$185.55	$185.55	$185.60
Purchase #2	$35.73	4.613%	$37.3782	$37.38	$37.40	$37.40
Purchase #3	$145.32	9.299%	$158.8333	$158.83	$158.85	$158.80
Purchase #4	$34.64	10.200%	$38.1733	$38.17	$38.15	$38.20
Purchase #5	$91.48	5.647%	$96.6459	$96.65	$96.65	$96.60
Purchase #6	$53.84	4.819%	$56.4345	$56.43	$56.45	$56.40
Purchase #7	$239.27	7.641%	$257.5526	$257.55	$257.55	$257.60
7 purchase totals =	$770.07		$830.5711	$830.56	$830.60	$830.60