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	$250.47	11.521%	$279.3266	$279.33	$279.35	$279.30
Purchase #2	$159.89	3.658%	$165.7388	$165.74	$165.75	$165.70
Purchase #3	$211.80	10.412%	$233.8526	$233.85	$233.85	$233.90
Purchase #4	$243.61	5.397%	$256.7576	$256.76	$256.75	$256.80
Purchase #5	$169.46	13.441%	$192.2371	$192.24	$192.25	$192.20
Purchase #6	$114.55	11.417%	$127.6282	$127.63	$127.65	$127.60
Purchase #7	$108.31	3.521%	$112.1236	$112.12	$112.10	$112.10
7 purchase totals =	$1,258.09		$1,367.6645	$1,367.67	$1,367.70	$1,367.60