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	$45.99	4.569%	$48.0913	$48.09	$48.10	$48.10
Purchase #2	$149.72	3.461%	$154.9018	$154.90	$154.90	$154.90
Purchase #3	$80.72	6.823%	$86.2275	$86.23	$86.25	$86.20
Purchase #4	$6.47	10.416%	$7.1439	$7.14	$7.15	$7.10
Purchase #5	$135.59	13.804%	$154.3068	$154.31	$154.30	$154.30
Purchase #6	$128.40	11.485%	$143.1467	$143.15	$143.15	$143.10
Purchase #7	$37.75	13.369%	$42.7968	$42.80	$42.80	$42.80
7 purchase totals =	$584.64		$636.6148	$636.62	$636.65	$636.50