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	$129.57	6.118%	$137.4971	$137.50	$137.50	$137.50
Purchase #2	$157.38	11.182%	$174.9782	$174.98	$175.00	$175.00
Purchase #3	$244.92	12.615%	$275.8167	$275.82	$275.80	$275.80
Purchase #4	$175.81	5.203%	$184.9574	$184.96	$184.95	$185.00
Purchase #5	$56.93	9.728%	$62.4682	$62.47	$62.45	$62.50
Purchase #6	$44.62	6.815%	$47.6609	$47.66	$47.65	$47.70
Purchase #7	$153.37	12.766%	$172.9492	$172.95	$172.95	$172.90
7 purchase totals =	$962.60		$1,056.3277	$1,056.34	$1,056.30	$1,056.40