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	$88.77	11.829%	$99.2706	$99.27	$99.25	$99.30
Purchase #2	$126.95	8.694%	$137.987	$137.99	$138.00	$138.00
Purchase #3	$245.88	3.828%	$255.2923	$255.29	$255.30	$255.30
Purchase #4	$98.75	13.218%	$111.8028	$111.80	$111.80	$111.80
Purchase #5	$225.74	7.234%	$242.07	$242.07	$242.05	$242.10
Purchase #6	$102.86	11.748%	$114.944	$114.94	$114.95	$114.90
Purchase #7	$240.37	6.177%	$255.2177	$255.22	$255.20	$255.20
7 purchase totals =	$1,129.32		$1,216.5844	$1,216.58	$1,216.55	$1,216.60