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	$131.46	9.653%	$144.1498	$144.15	$144.15	$144.10
Purchase #2	$205.25	12.171%	$230.231	$230.23	$230.25	$230.20
Purchase #3	$234.69	5.294%	$247.1145	$247.11	$247.10	$247.10
Purchase #4	$186.25	10.325%	$205.4803	$205.48	$205.50	$205.50
Purchase #5	$187.71	13.217%	$212.5196	$212.52	$212.50	$212.50
Purchase #6	$44.32	3.271%	$45.7697	$45.77	$45.75	$45.80
Purchase #7	$43.91	9.360%	$48.02	$48.02	$48.00	$48.00
7 purchase totals =	$1,033.59		$1,133.2849	$1,133.28	$1,133.25	$1,133.20