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	$106.54	4.330%	$111.1532	$111.15	$111.15	$111.20
Purchase #2	$109.76	9.566%	$120.2596	$120.26	$120.25	$120.30
Purchase #3	$46.78	12.547%	$52.6495	$52.65	$52.65	$52.60
Purchase #4	$81.42	11.395%	$90.6978	$90.70	$90.70	$90.70
Purchase #5	$56.64	13.556%	$64.3181	$64.32	$64.30	$64.30
Purchase #6	$109.95	13.337%	$124.614	$124.61	$124.60	$124.60
Purchase #7	$113.41	3.292%	$117.1435	$117.14	$117.15	$117.10
7 purchase totals =	$624.50		$680.8357	$680.83	$680.80	$680.80