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	$108.68	13.601%	$123.4616	$123.46	$123.45	$123.50
Purchase #2	$110.43	7.272%	$118.4605	$118.46	$118.45	$118.50
Purchase #3	$67.46	5.669%	$71.2843	$71.28	$71.30	$71.30
Purchase #4	$160.34	11.730%	$179.1479	$179.15	$179.15	$179.10
Purchase #5	$110.81	5.494%	$116.8979	$116.90	$116.90	$116.90
Purchase #6	$116.76	8.667%	$126.8796	$126.88	$126.90	$126.90
Purchase #7	$138.78	11.579%	$154.8493	$154.85	$154.85	$154.80
7 purchase totals =	$813.26		$890.9811	$890.98	$891.00	$891.00