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	$248.45	10.583%	$274.7435	$274.74	$274.75	$274.70
Purchase #2	$170.91	5.113%	$179.6486	$179.65	$179.65	$179.60
Purchase #3	$118.26	10.457%	$130.6264	$130.63	$130.65	$130.60
Purchase #4	$170.39	5.196%	$179.2435	$179.24	$179.25	$179.20
Purchase #5	$81.77	4.496%	$85.4464	$85.45	$85.45	$85.40
Purchase #6	$213.78	9.123%	$233.2831	$233.28	$233.30	$233.30
Purchase #7	$138.29	3.513%	$143.1481	$143.15	$143.15	$143.10
7 purchase totals =	$1,141.85		$1,226.1396	$1,226.14	$1,226.20	$1,225.90