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	$239.71	6.454%	$255.1809	$255.18	$255.20	$255.20
Purchase #2	$205.62	4.157%	$214.1676	$214.17	$214.15	$214.20
Purchase #3	$111.41	4.420%	$116.3343	$116.33	$116.35	$116.30
Purchase #4	$237.34	5.517%	$250.434	$250.43	$250.45	$250.40
Purchase #5	$100.77	8.797%	$109.6347	$109.63	$109.65	$109.60
Purchase #6	$35.49	11.805%	$39.6796	$39.68	$39.70	$39.70
Purchase #7	$99.46	4.840%	$104.2739	$104.27	$104.25	$104.30
7 purchase totals =	$1,029.80		$1,089.7050	$1,089.69	$1,089.75	$1,089.70