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	$96.27	3.798%	$99.9263	$99.93	$99.95	$99.90
Purchase #2	$144.75	6.104%	$153.5855	$153.59	$153.60	$153.60
Purchase #3	$91.91	12.342%	$103.2535	$103.25	$103.25	$103.30
Purchase #4	$149.74	11.873%	$167.5186	$167.52	$167.50	$167.50
Purchase #5	$114.97	12.743%	$129.6206	$129.62	$129.60	$129.60
Purchase #6	$102.74	8.382%	$111.3517	$111.35	$111.35	$111.40
Purchase #7	$16.66	9.721%	$18.2795	$18.28	$18.30	$18.30
7 purchase totals =	$717.04		$783.5357	$783.54	$783.55	$783.60