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	$43.97	13.680%	$49.9851	$49.99	$50.00	$50.00
Purchase #2	$16.56	9.325%	$18.1042	$18.10	$18.10	$18.10
Purchase #3	$227.88	6.122%	$241.8308	$241.83	$241.85	$241.80
Purchase #4	$41.31	6.112%	$43.8349	$43.83	$43.85	$43.80
Purchase #5	$106.97	12.705%	$120.5605	$120.56	$120.55	$120.60
Purchase #6	$51.30	6.771%	$54.7735	$54.77	$54.75	$54.80
Purchase #7	$18.28	13.501%	$20.748	$20.75	$20.75	$20.70
7 purchase totals =	$506.27		$549.8370	$549.83	$549.85	$549.80