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	$17.64	3.641%	$18.2823	$18.28	$18.30	$18.30
Purchase #2	$139.78	4.575%	$146.1749	$146.17	$146.15	$146.20
Purchase #3	$234.65	3.783%	$243.5268	$243.53	$243.55	$243.50
Purchase #4	$59.68	7.849%	$64.3643	$64.36	$64.35	$64.40
Purchase #5	$122.94	6.654%	$131.1204	$131.12	$131.10	$131.10
Purchase #6	$68.47	13.399%	$77.6443	$77.64	$77.65	$77.60
Purchase #7	$95.47	13.676%	$108.5265	$108.53	$108.55	$108.50
7 purchase totals =	$738.63		$789.6395	$789.63	$789.65	$789.60