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	$50.45	11.505%	$56.2543	$56.25	$56.25	$56.30
Purchase #2	$224.83	11.823%	$251.4117	$251.41	$251.40	$251.40
Purchase #3	$125.35	13.137%	$141.8172	$141.82	$141.80	$141.80
Purchase #4	$106.98	11.240%	$119.0046	$119.00	$119.00	$119.00
Purchase #5	$117.36	5.690%	$124.0378	$124.04	$124.05	$124.00
Purchase #6	$104.83	6.707%	$111.8609	$111.86	$111.85	$111.90
Purchase #7	$105.83	5.274%	$111.4115	$111.41	$111.40	$111.40
7 purchase totals =	$835.63		$915.7980	$915.79	$915.75	$915.80