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	$44.34	12.643%	$49.9459	$49.95	$49.95	$49.90
Purchase #2	$221.58	4.450%	$231.4403	$231.44	$231.45	$231.40
Purchase #3	$28.41	10.190%	$31.305	$31.31	$31.30	$31.30
Purchase #4	$89.77	11.803%	$100.3656	$100.37	$100.35	$100.40
Purchase #5	$52.74	8.518%	$57.2324	$57.23	$57.25	$57.20
Purchase #6	$104.93	4.734%	$109.8974	$109.90	$109.90	$109.90
Purchase #7	$56.39	5.404%	$59.4373	$59.44	$59.45	$59.40
7 purchase totals =	$598.16		$639.6239	$639.64	$639.65	$639.50