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	$68.56	13.861%	$78.0631	$78.06	$78.05	$78.10
Purchase #2	$180.60	4.697%	$189.0828	$189.08	$189.10	$189.10
Purchase #3	$160.94	5.863%	$170.3759	$170.38	$170.40	$170.40
Purchase #4	$115.62	11.194%	$128.5625	$128.56	$128.55	$128.60
Purchase #5	$142.27	4.611%	$148.8301	$148.83	$148.85	$148.80
Purchase #6	$128.63	13.363%	$145.8188	$145.82	$145.80	$145.80
Purchase #7	$40.57	11.251%	$45.1345	$45.13	$45.15	$45.10
7 purchase totals =	$837.19		$905.8677	$905.86	$905.90	$905.90