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	$36.68	10.482%	$40.5248	$40.52	$40.50	$40.50
Purchase #2	$126.63	4.615%	$132.474	$132.47	$132.45	$132.50
Purchase #3	$133.53	3.168%	$137.7602	$137.76	$137.75	$137.80
Purchase #4	$222.49	4.873%	$233.3319	$233.33	$233.35	$233.30
Purchase #5	$155.86	5.504%	$164.4385	$164.44	$164.45	$164.40
Purchase #6	$36.28	10.180%	$39.9733	$39.97	$39.95	$40.00
Purchase #7	$99.31	3.776%	$103.0599	$103.06	$103.05	$103.10
7 purchase totals =	$810.78		$851.5626	$851.55	$851.50	$851.60