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	$149.88	6.711%	$159.9384	$159.94	$159.95	$159.90
Purchase #2	$139.63	8.660%	$151.722	$151.72	$151.70	$151.70
Purchase #3	$42.60	9.233%	$46.5333	$46.53	$46.55	$46.50
Purchase #4	$188.93	5.558%	$199.4307	$199.43	$199.45	$199.40
Purchase #5	$239.81	5.598%	$253.2346	$253.23	$253.25	$253.20
Purchase #6	$146.42	4.114%	$152.4437	$152.44	$152.45	$152.40
Purchase #7	$14.58	3.604%	$15.1055	$15.11	$15.10	$15.10
7 purchase totals =	$921.85		$978.4082	$978.40	$978.45	$978.20