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	$217.50	6.131%	$230.8349	$230.83	$230.85	$230.80
Purchase #2	$134.88	5.599%	$142.4319	$142.43	$142.45	$142.40
Purchase #3	$17.76	5.267%	$18.6954	$18.70	$18.70	$18.70
Purchase #4	$73.57	12.343%	$82.6507	$82.65	$82.65	$82.70
Purchase #5	$38.36	13.537%	$43.5528	$43.55	$43.55	$43.60
Purchase #6	$62.61	4.310%	$65.3085	$65.31	$65.30	$65.30
Purchase #7	$91.58	5.795%	$96.8871	$96.89	$96.90	$96.90
7 purchase totals =	$636.26		$680.3613	$680.36	$680.40	$680.40