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	$61.97	5.819%	$65.576	$65.58	$65.60	$65.60
Purchase #2	$225.67	4.275%	$235.3174	$235.32	$235.30	$235.30
Purchase #3	$208.88	6.528%	$222.5157	$222.52	$222.50	$222.50
Purchase #4	$248.36	3.235%	$256.3944	$256.39	$256.40	$256.40
Purchase #5	$139.76	13.649%	$158.8358	$158.84	$158.85	$158.80
Purchase #6	$80.67	13.260%	$91.3668	$91.37	$91.35	$91.40
Purchase #7	$109.99	4.201%	$114.6107	$114.61	$114.60	$114.60
7 purchase totals =	$1,075.30		$1,144.6168	$1,144.63	$1,144.60	$1,144.60