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	$242.32	10.820%	$268.539	$268.54	$268.55	$268.50
Purchase #2	$67.69	7.208%	$72.5691	$72.57	$72.55	$72.60
Purchase #3	$42.41	8.142%	$45.863	$45.86	$45.85	$45.90
Purchase #4	$121.69	11.831%	$136.0871	$136.09	$136.10	$136.10
Purchase #5	$53.71	5.584%	$56.7092	$56.71	$56.70	$56.70
Purchase #6	$30.70	12.279%	$34.4697	$34.47	$34.45	$34.50
Purchase #7	$178.58	5.185%	$187.8394	$187.84	$187.85	$187.80
7 purchase totals =	$737.10		$802.0765	$802.08	$802.05	$802.10