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	$19.66	3.653%	$20.3782	$20.38	$20.40	$20.40
Purchase #2	$95.46	6.137%	$101.3184	$101.32	$101.30	$101.30
Purchase #3	$208.52	3.345%	$215.495	$215.50	$215.50	$215.50
Purchase #4	$210.78	6.422%	$224.3163	$224.32	$224.30	$224.30
Purchase #5	$162.75	6.525%	$173.3694	$173.37	$173.35	$173.40
Purchase #6	$49.51	9.814%	$54.3689	$54.37	$54.35	$54.40
Purchase #7	$12.48	7.447%	$13.4094	$13.41	$13.40	$13.40
7 purchase totals =	$759.16		$802.6556	$802.67	$802.60	$802.70