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	$89.32	11.805%	$99.8642	$99.86	$99.85	$99.90
Purchase #2	$230.43	9.793%	$252.996	$253.00	$253.00	$253.00
Purchase #3	$150.91	11.239%	$167.8708	$167.87	$167.85	$167.90
Purchase #4	$41.89	10.232%	$46.1762	$46.18	$46.20	$46.20
Purchase #5	$43.88	6.492%	$46.7287	$46.73	$46.75	$46.70
Purchase #6	$146.75	13.685%	$166.8327	$166.83	$166.85	$166.80
Purchase #7	$6.83	13.309%	$7.739	$7.74	$7.75	$7.70
7 purchase totals =	$710.01		$788.2076	$788.21	$788.25	$788.20