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	$159.57	11.793%	$178.3881	$178.39	$178.40	$178.40
Purchase #2	$205.45	4.315%	$214.3152	$214.32	$214.30	$214.30
Purchase #3	$216.74	5.762%	$229.2286	$229.23	$229.25	$229.20
Purchase #4	$31.96	4.763%	$33.4823	$33.48	$33.50	$33.50
Purchase #5	$50.79	13.387%	$57.5893	$57.59	$57.60	$57.60
Purchase #6	$121.71	4.382%	$127.0433	$127.04	$127.05	$127.00
Purchase #7	$55.65	10.145%	$61.2957	$61.30	$61.30	$61.30
7 purchase totals =	$841.87		$901.3425	$901.35	$901.40	$901.30