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	$115.54	9.247%	$126.224	$126.22	$126.20	$126.20
Purchase #2	$64.37	11.152%	$71.5485	$71.55	$71.55	$71.50
Purchase #3	$157.72	4.514%	$164.8395	$164.84	$164.85	$164.80
Purchase #4	$99.64	10.526%	$110.1281	$110.13	$110.15	$110.10
Purchase #5	$17.49	13.703%	$19.8867	$19.89	$19.90	$19.90
Purchase #6	$124.78	6.449%	$132.8271	$132.83	$132.85	$132.80
Purchase #7	$39.73	8.111%	$42.9525	$42.95	$42.95	$43.00
7 purchase totals =	$619.27		$668.4064	$668.41	$668.45	$668.30