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	$84.70	6.298%	$90.0344	$90.03	$90.05	$90.00
Purchase #2	$27.88	6.801%	$29.7761	$29.78	$29.80	$29.80
Purchase #3	$185.52	6.147%	$196.9239	$196.92	$196.90	$196.90
Purchase #4	$80.72	9.223%	$88.1648	$88.16	$88.15	$88.20
Purchase #5	$125.41	9.593%	$137.4406	$137.44	$137.45	$137.40
Purchase #6	$101.48	9.551%	$111.1724	$111.17	$111.15	$111.20
Purchase #7	$132.91	6.329%	$141.3219	$141.32	$141.30	$141.30
7 purchase totals =	$738.62		$794.8341	$794.82	$794.80	$794.80