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	$61.94	7.577%	$66.6332	$66.63	$66.65	$66.60
Purchase #2	$59.27	8.363%	$64.2268	$64.23	$64.25	$64.20
Purchase #3	$129.34	6.470%	$137.7083	$137.71	$137.70	$137.70
Purchase #4	$35.99	6.599%	$38.365	$38.37	$38.35	$38.40
Purchase #5	$237.97	7.383%	$255.5393	$255.54	$255.55	$255.50
Purchase #6	$199.30	3.612%	$206.4987	$206.50	$206.50	$206.50
Purchase #7	$207.26	12.550%	$233.2711	$233.27	$233.25	$233.30
7 purchase totals =	$931.07		$1,002.2424	$1,002.25	$1,002.25	$1,002.20