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	$156.92	9.689%	$172.124	$172.12	$172.10	$172.10
Purchase #2	$92.48	8.435%	$100.2807	$100.28	$100.30	$100.30
Purchase #3	$86.41	4.125%	$89.9744	$89.97	$89.95	$90.00
Purchase #4	$48.75	11.512%	$54.3621	$54.36	$54.35	$54.40
Purchase #5	$47.83	12.870%	$53.9857	$53.99	$54.00	$54.00
Purchase #6	$143.49	7.862%	$154.7712	$154.77	$154.75	$154.80
Purchase #7	$153.86	7.448%	$165.3195	$165.32	$165.30	$165.30
7 purchase totals =	$729.74		$790.8176	$790.81	$790.75	$790.90