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	$20.74	3.395%	$21.4441	$21.44	$21.45	$21.40
Purchase #2	$226.89	11.348%	$252.6375	$252.64	$252.65	$252.60
Purchase #3	$94.71	11.150%	$105.2702	$105.27	$105.25	$105.30
Purchase #4	$239.65	3.808%	$248.7759	$248.78	$248.80	$248.80
Purchase #5	$188.27	6.213%	$199.9672	$199.97	$199.95	$200.00
Purchase #6	$158.57	5.254%	$166.9013	$166.90	$166.90	$166.90
Purchase #7	$54.89	8.129%	$59.352	$59.35	$59.35	$59.40
7 purchase totals =	$983.72		$1,054.3482	$1,054.35	$1,054.35	$1,054.40