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	$31.58	9.506%	$34.582	$34.58	$34.60	$34.60
Purchase #2	$105.71	6.648%	$112.7376	$112.74	$112.75	$112.70
Purchase #3	$95.76	5.144%	$100.6859	$100.69	$100.70	$100.70
Purchase #4	$130.97	12.107%	$146.8265	$146.83	$146.85	$146.80
Purchase #5	$79.53	12.170%	$89.2088	$89.21	$89.20	$89.20
Purchase #6	$43.79	13.755%	$49.8133	$49.81	$49.80	$49.80
Purchase #7	$33.84	9.431%	$37.0315	$37.03	$37.05	$37.00
7 purchase totals =	$521.18		$570.8856	$570.89	$570.95	$570.80