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	$38.88	10.169%	$42.8337	$42.83	$42.85	$42.80
Purchase #2	$29.54	3.573%	$30.5955	$30.60	$30.60	$30.60
Purchase #3	$168.29	13.456%	$190.9351	$190.94	$190.95	$190.90
Purchase #4	$53.68	9.572%	$58.8182	$58.82	$58.80	$58.80
Purchase #5	$65.50	10.445%	$72.3415	$72.34	$72.35	$72.30
Purchase #6	$41.48	5.380%	$43.7116	$43.71	$43.70	$43.70
Purchase #7	$149.88	7.137%	$160.5769	$160.58	$160.60	$160.60
7 purchase totals =	$547.25		$599.8125	$599.82	$599.85	$599.70