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	$37.87	12.240%	$42.5053	$42.51	$42.50	$42.50
Purchase #2	$124.85	7.279%	$133.9378	$133.94	$133.95	$133.90
Purchase #3	$152.87	13.158%	$172.9846	$172.98	$173.00	$173.00
Purchase #4	$141.48	8.668%	$153.7435	$153.74	$153.75	$153.70
Purchase #5	$82.87	7.804%	$89.3372	$89.34	$89.35	$89.30
Purchase #6	$176.66	9.651%	$193.7095	$193.71	$193.70	$193.70
Purchase #7	$102.28	6.754%	$109.188	$109.19	$109.20	$109.20
7 purchase totals =	$818.88		$895.4059	$895.41	$895.45	$895.30