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	$80.27	12.344%	$90.1785	$90.18	$90.20	$90.20
Purchase #2	$115.26	10.609%	$127.4879	$127.49	$127.50	$127.50
Purchase #3	$173.95	8.264%	$188.3252	$188.33	$188.35	$188.30
Purchase #4	$187.78	13.182%	$212.5332	$212.53	$212.55	$212.50
Purchase #5	$222.70	8.827%	$242.3577	$242.36	$242.35	$242.40
Purchase #6	$27.89	5.387%	$29.3924	$29.39	$29.40	$29.40
Purchase #7	$58.43	10.341%	$64.4722	$64.47	$64.45	$64.50
7 purchase totals =	$866.28		$954.7471	$954.75	$954.80	$954.80