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	$19.29	4.118%	$20.0844	$20.08	$20.10	$20.10
Purchase #2	$50.87	7.563%	$54.7173	$54.72	$54.70	$54.70
Purchase #3	$194.29	9.427%	$212.6057	$212.61	$212.60	$212.60
Purchase #4	$121.76	3.574%	$126.1117	$126.11	$126.10	$126.10
Purchase #5	$171.61	4.579%	$179.468	$179.47	$179.45	$179.50
Purchase #6	$85.89	5.683%	$90.7711	$90.77	$90.75	$90.80
Purchase #7	$238.92	9.855%	$262.4656	$262.47	$262.45	$262.50
7 purchase totals =	$882.63		$946.2238	$946.23	$946.15	$946.30