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	$152.55	3.236%	$157.4865	$157.49	$157.50	$157.50
Purchase #2	$52.57	3.333%	$54.3222	$54.32	$54.30	$54.30
Purchase #3	$250.27	11.570%	$279.2262	$279.23	$279.25	$279.20
Purchase #4	$101.87	11.195%	$113.2743	$113.27	$113.25	$113.30
Purchase #5	$160.66	8.288%	$173.9755	$173.98	$174.00	$174.00
Purchase #6	$91.31	10.441%	$100.8437	$100.84	$100.85	$100.80
Purchase #7	$207.32	9.552%	$227.1232	$227.12	$227.10	$227.10
7 purchase totals =	$1,016.55		$1,106.2516	$1,106.25	$1,106.25	$1,106.20