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	$30.56	11.735%	$34.1462	$34.15	$34.15	$34.10
Purchase #2	$64.87	11.564%	$72.3716	$72.37	$72.35	$72.40
Purchase #3	$11.62	8.467%	$12.6039	$12.60	$12.60	$12.60
Purchase #4	$152.68	13.361%	$173.0796	$173.08	$173.10	$173.10
Purchase #5	$57.83	7.860%	$62.3754	$62.38	$62.40	$62.40
Purchase #6	$220.33	11.448%	$245.5534	$245.55	$245.55	$245.60
Purchase #7	$122.71	4.526%	$128.2639	$128.26	$128.25	$128.30
7 purchase totals =	$660.60		$728.3940	$728.39	$728.40	$728.50