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	$245.89	13.666%	$279.4933	$279.49	$279.50	$279.50
Purchase #2	$233.37	9.299%	$255.0711	$255.07	$255.05	$255.10
Purchase #3	$122.60	11.303%	$136.4575	$136.46	$136.45	$136.50
Purchase #4	$99.32	6.182%	$105.46	$105.46	$105.45	$105.50
Purchase #5	$237.73	11.296%	$264.584	$264.58	$264.60	$264.60
Purchase #6	$235.94	8.419%	$255.8038	$255.80	$255.80	$255.80
Purchase #7	$16.75	3.568%	$17.3476	$17.35	$17.35	$17.30
7 purchase totals =	$1,191.60		$1,314.2173	$1,314.21	$1,314.20	$1,314.30