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	$49.79	6.213%	$52.8835	$52.88	$52.90	$52.90
Purchase #2	$239.53	11.142%	$266.2184	$266.22	$266.20	$266.20
Purchase #3	$167.45	10.582%	$185.1696	$185.17	$185.15	$185.20
Purchase #4	$114.38	11.284%	$127.2866	$127.29	$127.30	$127.30
Purchase #5	$154.99	8.352%	$167.9348	$167.93	$167.95	$167.90
Purchase #6	$176.81	13.259%	$200.2532	$200.25	$200.25	$200.30
Purchase #7	$105.26	12.275%	$118.1807	$118.18	$118.20	$118.20
7 purchase totals =	$1,008.21		$1,117.9268	$1,117.92	$1,117.95	$1,118.00