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	$48.60	12.316%	$54.5856	$54.59	$54.60	$54.60
Purchase #2	$137.93	3.845%	$143.2334	$143.23	$143.25	$143.20
Purchase #3	$80.30	12.400%	$90.2572	$90.26	$90.25	$90.30
Purchase #4	$201.98	4.131%	$210.3238	$210.32	$210.30	$210.30
Purchase #5	$152.68	11.573%	$170.3497	$170.35	$170.35	$170.30
Purchase #6	$32.79	13.391%	$37.1809	$37.18	$37.20	$37.20
Purchase #7	$135.94	13.629%	$154.4673	$154.47	$154.45	$154.50
7 purchase totals =	$790.22		$860.3979	$860.40	$860.40	$860.40