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	$73.80	7.704%	$79.4856	$79.49	$79.50	$79.50
Purchase #2	$190.29	13.159%	$215.3303	$215.33	$215.35	$215.30
Purchase #3	$249.28	11.250%	$277.324	$277.32	$277.30	$277.30
Purchase #4	$64.37	3.140%	$66.3912	$66.39	$66.40	$66.40
Purchase #5	$29.35	13.613%	$33.3454	$33.35	$33.35	$33.30
Purchase #6	$139.27	10.192%	$153.4644	$153.46	$153.45	$153.50
Purchase #7	$83.76	6.341%	$89.0712	$89.07	$89.05	$89.10
7 purchase totals =	$830.12		$914.4121	$914.41	$914.40	$914.40