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	$179.28	5.455%	$189.0597	$189.06	$189.05	$189.10
Purchase #2	$41.54	11.338%	$46.2498	$46.25	$46.25	$46.20
Purchase #3	$145.47	6.772%	$155.3212	$155.32	$155.30	$155.30
Purchase #4	$15.81	9.481%	$17.3089	$17.31	$17.30	$17.30
Purchase #5	$127.52	11.231%	$141.8418	$141.84	$141.85	$141.80
Purchase #6	$81.52	9.680%	$89.4111	$89.41	$89.40	$89.40
Purchase #7	$32.33	13.285%	$36.625	$36.63	$36.65	$36.60
7 purchase totals =	$623.47		$675.8175	$675.82	$675.80	$675.70