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	$41.30	5.381%	$43.5224	$43.52	$43.50	$43.50
Purchase #2	$150.41	4.376%	$156.9919	$156.99	$157.00	$157.00
Purchase #3	$68.44	7.112%	$73.3075	$73.31	$73.30	$73.30
Purchase #4	$109.65	12.567%	$123.4297	$123.43	$123.45	$123.40
Purchase #5	$9.69	9.532%	$10.6137	$10.61	$10.60	$10.60
Purchase #6	$123.34	9.262%	$134.7638	$134.76	$134.75	$134.80
Purchase #7	$90.85	10.191%	$100.1085	$100.11	$100.10	$100.10
7 purchase totals =	$593.68		$642.7375	$642.73	$642.70	$642.70