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	$35.69	11.200%	$39.6873	$39.69	$39.70	$39.70
Purchase #2	$58.98	10.847%	$65.3776	$65.38	$65.40	$65.40
Purchase #3	$85.54	6.287%	$90.9179	$90.92	$90.90	$90.90
Purchase #4	$234.59	4.198%	$244.4381	$244.44	$244.45	$244.40
Purchase #5	$118.70	11.459%	$132.3018	$132.30	$132.30	$132.30
Purchase #6	$127.86	7.483%	$137.4278	$137.43	$137.45	$137.40
Purchase #7	$153.93	9.240%	$168.1531	$168.15	$168.15	$168.20
7 purchase totals =	$815.29		$878.3036	$878.31	$878.35	$878.30