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	$131.96	12.388%	$148.3072	$148.31	$148.30	$148.30
Purchase #2	$248.43	7.787%	$267.7752	$267.78	$267.80	$267.80
Purchase #3	$235.30	8.108%	$254.3781	$254.38	$254.40	$254.40
Purchase #4	$127.79	12.348%	$143.5695	$143.57	$143.55	$143.60
Purchase #5	$83.83	5.705%	$88.6125	$88.61	$88.60	$88.60
Purchase #6	$59.59	5.239%	$62.7119	$62.71	$62.70	$62.70
Purchase #7	$216.26	11.161%	$240.3968	$240.40	$240.40	$240.40
7 purchase totals =	$1,103.16		$1,205.7512	$1,205.76	$1,205.75	$1,205.80