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	$26.74	12.705%	$30.1373	$30.14	$30.15	$30.10
Purchase #2	$123.35	6.382%	$131.2222	$131.22	$131.20	$131.20
Purchase #3	$235.80	12.599%	$265.5084	$265.51	$265.50	$265.50
Purchase #4	$113.81	8.820%	$123.848	$123.85	$123.85	$123.80
Purchase #5	$44.82	13.501%	$50.8711	$50.87	$50.85	$50.90
Purchase #6	$94.46	11.265%	$105.1009	$105.10	$105.10	$105.10
Purchase #7	$9.58	3.439%	$9.9095	$9.91	$9.90	$9.90
7 purchase totals =	$648.56		$716.5974	$716.60	$716.55	$716.50