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	$85.73	6.262%	$91.0984	$91.10	$91.10	$91.10
Purchase #2	$51.71	5.307%	$54.4542	$54.45	$54.45	$54.50
Purchase #3	$153.91	3.245%	$158.9044	$158.90	$158.90	$158.90
Purchase #4	$117.45	11.154%	$130.5504	$130.55	$130.55	$130.60
Purchase #5	$157.97	8.733%	$171.7655	$171.77	$171.75	$171.80
Purchase #6	$41.66	5.341%	$43.8851	$43.89	$43.90	$43.90
Purchase #7	$185.92	3.328%	$192.1074	$192.11	$192.10	$192.10
7 purchase totals =	$794.35		$842.7654	$842.77	$842.75	$842.90