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	$93.86	5.185%	$98.7266	$98.73	$98.75	$98.70
Purchase #2	$132.49	7.555%	$142.4996	$142.50	$142.50	$142.50
Purchase #3	$210.40	9.559%	$230.5121	$230.51	$230.50	$230.50
Purchase #4	$242.38	5.654%	$256.0842	$256.08	$256.10	$256.10
Purchase #5	$33.88	12.247%	$38.0293	$38.03	$38.05	$38.00
Purchase #6	$52.93	13.580%	$60.1179	$60.12	$60.10	$60.10
Purchase #7	$142.63	7.160%	$152.8423	$152.84	$152.85	$152.80
7 purchase totals =	$908.57		$978.8120	$978.81	$978.85	$978.70