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	$40.41	8.577%	$43.876	$43.88	$43.90	$43.90
Purchase #2	$96.60	12.830%	$108.9938	$108.99	$109.00	$109.00
Purchase #3	$18.52	11.653%	$20.6781	$20.68	$20.70	$20.70
Purchase #4	$214.47	6.667%	$228.7687	$228.77	$228.75	$228.80
Purchase #5	$31.31	11.417%	$34.8847	$34.88	$34.90	$34.90
Purchase #6	$98.99	10.363%	$109.2483	$109.25	$109.25	$109.20
Purchase #7	$49.97	6.809%	$53.3725	$53.37	$53.35	$53.40
7 purchase totals =	$550.27		$599.8221	$599.82	$599.85	$599.90