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	$138.48	8.318%	$149.9988	$150.00	$150.00	$150.00
Purchase #2	$19.72	5.102%	$20.7261	$20.73	$20.75	$20.70
Purchase #3	$223.30	13.234%	$252.8515	$252.85	$252.85	$252.90
Purchase #4	$221.86	9.131%	$242.118	$242.12	$242.10	$242.10
Purchase #5	$79.96	10.709%	$88.5229	$88.52	$88.50	$88.50
Purchase #6	$239.96	7.732%	$258.5137	$258.51	$258.50	$258.50
Purchase #7	$45.82	10.256%	$50.5193	$50.52	$50.50	$50.50
7 purchase totals =	$969.10		$1,063.2503	$1,063.25	$1,063.20	$1,063.20