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	$17.80	11.269%	$19.8059	$19.81	$19.80	$19.80
Purchase #2	$131.79	13.243%	$149.2429	$149.24	$149.25	$149.20
Purchase #3	$52.75	3.521%	$54.6073	$54.61	$54.60	$54.60
Purchase #4	$167.62	12.138%	$187.9657	$187.97	$187.95	$188.00
Purchase #5	$98.45	13.127%	$111.3735	$111.37	$111.35	$111.40
Purchase #6	$127.75	11.450%	$142.3774	$142.38	$142.40	$142.40
Purchase #7	$79.38	11.661%	$88.6365	$88.64	$88.65	$88.60
7 purchase totals =	$675.54		$754.0092	$754.02	$754.00	$754.00