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	$50.45	11.461%	$56.2321	$56.23	$56.25	$56.20
Purchase #2	$32.80	4.585%	$34.3039	$34.30	$34.30	$34.30
Purchase #3	$84.59	6.710%	$90.266	$90.27	$90.25	$90.30
Purchase #4	$57.92	4.161%	$60.3301	$60.33	$60.35	$60.30
Purchase #5	$176.52	6.178%	$187.4254	$187.43	$187.45	$187.40
Purchase #6	$139.40	10.322%	$153.7889	$153.79	$153.80	$153.80
Purchase #7	$76.78	8.174%	$83.056	$83.06	$83.05	$83.10
7 purchase totals =	$618.46		$665.4024	$665.41	$665.45	$665.40