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	$171.81	9.573%	$188.2574	$188.26	$188.25	$188.30
Purchase #2	$153.92	9.452%	$168.4685	$168.47	$168.45	$168.50
Purchase #3	$238.41	8.687%	$259.1207	$259.12	$259.10	$259.10
Purchase #4	$112.47	9.618%	$123.2874	$123.29	$123.30	$123.30
Purchase #5	$10.74	4.714%	$11.2463	$11.25	$11.25	$11.20
Purchase #6	$21.90	8.700%	$23.8053	$23.81	$23.80	$23.80
Purchase #7	$25.76	6.819%	$27.5166	$27.52	$27.50	$27.50
7 purchase totals =	$735.01		$801.7022	$801.72	$801.65	$801.70