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	$35.61	5.154%	$37.4453	$37.45	$37.45	$37.40
Purchase #2	$194.91	12.752%	$219.7649	$219.76	$219.75	$219.80
Purchase #3	$64.87	7.752%	$69.8987	$69.90	$69.90	$69.90
Purchase #4	$120.96	5.476%	$127.5838	$127.58	$127.60	$127.60
Purchase #5	$11.80	3.252%	$12.1837	$12.18	$12.20	$12.20
Purchase #6	$29.78	9.480%	$32.6031	$32.60	$32.60	$32.60
Purchase #7	$250.40	11.675%	$279.6342	$279.63	$279.65	$279.60
7 purchase totals =	$708.33		$779.1137	$779.10	$779.15	$779.10