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	$206.81	10.369%	$228.2541	$228.25	$228.25	$228.30
Purchase #2	$152.37	13.323%	$172.6703	$172.67	$172.65	$172.70
Purchase #3	$92.27	9.343%	$100.8908	$100.89	$100.90	$100.90
Purchase #4	$18.82	11.471%	$20.9788	$20.98	$21.00	$21.00
Purchase #5	$55.93	7.352%	$60.042	$60.04	$60.05	$60.00
Purchase #6	$164.82	4.627%	$172.4462	$172.45	$172.45	$172.40
Purchase #7	$149.90	3.772%	$155.5542	$155.55	$155.55	$155.60
7 purchase totals =	$840.92		$910.8364	$910.83	$910.85	$910.90