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	$51.29	8.857%	$55.8328	$55.83	$55.85	$55.80
Purchase #2	$141.30	11.566%	$157.6428	$157.64	$157.65	$157.60
Purchase #3	$242.33	4.533%	$253.3148	$253.31	$253.30	$253.30
Purchase #4	$46.51	5.741%	$49.1801	$49.18	$49.20	$49.20
Purchase #5	$207.87	8.151%	$224.8135	$224.81	$224.80	$224.80
Purchase #6	$204.39	9.240%	$223.2756	$223.28	$223.30	$223.30
Purchase #7	$39.76	7.123%	$42.5921	$42.59	$42.60	$42.60
7 purchase totals =	$933.45		$1,006.6517	$1,006.64	$1,006.70	$1,006.60