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	$249.64	9.268%	$272.7766	$272.78	$272.80	$272.80
Purchase #2	$178.45	7.863%	$192.4815	$192.48	$192.50	$192.50
Purchase #3	$201.58	10.806%	$223.3627	$223.36	$223.35	$223.40
Purchase #4	$129.94	4.679%	$136.0199	$136.02	$136.00	$136.00
Purchase #5	$110.65	11.291%	$123.1435	$123.14	$123.15	$123.10
Purchase #6	$125.57	9.552%	$137.5644	$137.56	$137.55	$137.60
Purchase #7	$91.42	9.332%	$99.9513	$99.95	$99.95	$100.00
7 purchase totals =	$1,087.25		$1,185.2999	$1,185.29	$1,185.30	$1,185.40