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	$171.97	5.533%	$181.4851	$181.49	$181.50	$181.50
Purchase #2	$170.88	12.264%	$191.8367	$191.84	$191.85	$191.80
Purchase #3	$29.27	9.581%	$32.0744	$32.07	$32.05	$32.10
Purchase #4	$24.60	6.298%	$26.1493	$26.15	$26.15	$26.10
Purchase #5	$137.87	12.368%	$154.9218	$154.92	$154.90	$154.90
Purchase #6	$116.72	9.457%	$127.7582	$127.76	$127.75	$127.80
Purchase #7	$216.72	6.725%	$231.2944	$231.29	$231.30	$231.30
7 purchase totals =	$868.03		$945.5199	$945.52	$945.50	$945.50