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	$50.32	6.337%	$53.5088	$53.51	$53.50	$53.50
Purchase #2	$231.77	4.708%	$242.6817	$242.68	$242.70	$242.70
Purchase #3	$82.89	10.792%	$91.8355	$91.84	$91.85	$91.80
Purchase #4	$153.70	9.549%	$168.3768	$168.38	$168.40	$168.40
Purchase #5	$58.41	11.287%	$65.0027	$65.00	$65.00	$65.00
Purchase #6	$121.45	13.349%	$137.6624	$137.66	$137.65	$137.70
Purchase #7	$60.32	10.656%	$66.7477	$66.75	$66.75	$66.70
7 purchase totals =	$758.86		$825.8156	$825.82	$825.85	$825.80