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	$40.80	7.121%	$43.7054	$43.71	$43.70	$43.70
Purchase #2	$107.80	5.212%	$113.4185	$113.42	$113.40	$113.40
Purchase #3	$242.90	13.590%	$275.9101	$275.91	$275.90	$275.90
Purchase #4	$149.74	5.794%	$158.4159	$158.42	$158.40	$158.40
Purchase #5	$81.46	10.873%	$90.3171	$90.32	$90.30	$90.30
Purchase #6	$165.72	13.703%	$188.4286	$188.43	$188.45	$188.40
Purchase #7	$33.60	12.820%	$37.9075	$37.91	$37.90	$37.90
7 purchase totals =	$822.02		$908.1031	$908.12	$908.05	$908.00