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	$29.52	7.798%	$31.822	$31.82	$31.80	$31.80
Purchase #2	$132.27	5.166%	$139.1031	$139.10	$139.10	$139.10
Purchase #3	$128.95	6.504%	$137.3369	$137.34	$137.35	$137.30
Purchase #4	$244.98	8.427%	$265.6245	$265.62	$265.60	$265.60
Purchase #5	$154.77	11.316%	$172.2838	$172.28	$172.30	$172.30
Purchase #6	$48.45	5.540%	$51.1341	$51.13	$51.15	$51.10
Purchase #7	$188.60	5.425%	$198.8316	$198.83	$198.85	$198.80
7 purchase totals =	$927.54		$996.1360	$996.12	$996.15	$996.00