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	$237.72	9.130%	$259.4238	$259.42	$259.40	$259.40
Purchase #2	$178.32	9.670%	$195.5635	$195.56	$195.55	$195.60
Purchase #3	$19.83	13.181%	$22.4438	$22.44	$22.45	$22.40
Purchase #4	$62.59	8.466%	$67.8889	$67.89	$67.90	$67.90
Purchase #5	$91.57	11.616%	$102.2068	$102.21	$102.20	$102.20
Purchase #6	$164.80	12.422%	$185.2715	$185.27	$185.25	$185.30
Purchase #7	$48.73	3.269%	$50.323	$50.32	$50.30	$50.30
7 purchase totals =	$803.56		$883.1213	$883.11	$883.05	$883.10