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	$77.76	6.317%	$82.6721	$82.67	$82.65	$82.70
Purchase #2	$141.61	10.463%	$156.4267	$156.43	$156.45	$156.40
Purchase #3	$146.66	7.381%	$157.485	$157.49	$157.50	$157.50
Purchase #4	$15.28	11.373%	$17.0178	$17.02	$17.00	$17.00
Purchase #5	$143.46	8.697%	$155.9367	$155.94	$155.95	$155.90
Purchase #6	$151.73	8.182%	$164.1445	$164.14	$164.15	$164.10
Purchase #7	$36.63	9.615%	$40.152	$40.15	$40.15	$40.20
7 purchase totals =	$713.13		$773.8348	$773.84	$773.85	$773.80