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	$48.71	12.236%	$54.6702	$54.67	$54.65	$54.70
Purchase #2	$159.58	4.761%	$167.1776	$167.18	$167.20	$167.20
Purchase #3	$156.81	7.239%	$168.1615	$168.16	$168.15	$168.20
Purchase #4	$144.71	6.216%	$153.7052	$153.71	$153.70	$153.70
Purchase #5	$141.38	6.406%	$150.4368	$150.44	$150.45	$150.40
Purchase #6	$152.54	4.354%	$159.1816	$159.18	$159.20	$159.20
Purchase #7	$128.60	13.757%	$146.2915	$146.29	$146.30	$146.30
7 purchase totals =	$932.33		$999.6244	$999.63	$999.65	$999.70