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	$33.66	12.873%	$37.9931	$37.99	$38.00	$38.00
Purchase #2	$48.95	11.353%	$54.5073	$54.51	$54.50	$54.50
Purchase #3	$163.50	5.365%	$172.2718	$172.27	$172.25	$172.30
Purchase #4	$54.74	11.752%	$61.173	$61.17	$61.15	$61.20
Purchase #5	$218.46	4.583%	$228.472	$228.47	$228.45	$228.50
Purchase #6	$158.62	13.518%	$180.0623	$180.06	$180.05	$180.10
Purchase #7	$13.78	9.843%	$15.1364	$15.14	$15.15	$15.10
7 purchase totals =	$691.71		$749.6159	$749.61	$749.55	$749.70