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	$12.25	5.301%	$12.8994	$12.90	$12.90	$12.90
Purchase #2	$35.31	10.385%	$38.9769	$38.98	$39.00	$39.00
Purchase #3	$243.60	11.412%	$271.3996	$271.40	$271.40	$271.40
Purchase #4	$127.95	11.147%	$142.2126	$142.21	$142.20	$142.20
Purchase #5	$227.58	13.410%	$258.0985	$258.10	$258.10	$258.10
Purchase #6	$119.53	3.577%	$123.8056	$123.81	$123.80	$123.80
Purchase #7	$35.26	12.764%	$39.7606	$39.76	$39.75	$39.80
7 purchase totals =	$801.48		$887.1532	$887.16	$887.15	$887.20