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	$249.43	10.349%	$275.2435	$275.24	$275.25	$275.20
Purchase #2	$163.53	5.463%	$172.4636	$172.46	$172.45	$172.50
Purchase #3	$11.59	7.452%	$12.4537	$12.45	$12.45	$12.50
Purchase #4	$101.55	9.336%	$111.0307	$111.03	$111.05	$111.00
Purchase #5	$8.76	7.732%	$9.4373	$9.44	$9.45	$9.40
Purchase #6	$33.68	13.850%	$38.3447	$38.34	$38.35	$38.30
Purchase #7	$204.27	3.423%	$211.2622	$211.26	$211.25	$211.30
7 purchase totals =	$772.81		$830.2357	$830.22	$830.25	$830.20