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	$54.85	13.454%	$62.2295	$62.23	$62.25	$62.20
Purchase #2	$219.57	5.115%	$230.801	$230.80	$230.80	$230.80
Purchase #3	$54.65	9.131%	$59.6401	$59.64	$59.65	$59.60
Purchase #4	$42.90	10.658%	$47.4723	$47.47	$47.45	$47.50
Purchase #5	$250.36	11.807%	$279.92	$279.92	$279.90	$279.90
Purchase #6	$32.94	13.452%	$37.3711	$37.37	$37.35	$37.40
Purchase #7	$132.46	11.372%	$147.5234	$147.52	$147.50	$147.50
7 purchase totals =	$787.73		$864.9574	$864.95	$864.90	$864.90