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	$139.43	4.242%	$145.3446	$145.34	$145.35	$145.30
Purchase #2	$139.72	11.616%	$155.9499	$155.95	$155.95	$155.90
Purchase #3	$13.96	13.403%	$15.8311	$15.83	$15.85	$15.80
Purchase #4	$118.35	7.497%	$127.2227	$127.22	$127.20	$127.20
Purchase #5	$57.96	3.831%	$60.1804	$60.18	$60.20	$60.20
Purchase #6	$111.92	13.488%	$127.0158	$127.02	$127.00	$127.00
Purchase #7	$207.62	8.271%	$224.7923	$224.79	$224.80	$224.80
7 purchase totals =	$788.96		$856.3368	$856.33	$856.35	$856.20