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	$40.42	3.469%	$41.8222	$41.82	$41.80	$41.80
Purchase #2	$162.87	12.339%	$182.9665	$182.97	$182.95	$183.00
Purchase #3	$160.48	7.730%	$172.8851	$172.89	$172.90	$172.90
Purchase #4	$100.76	8.242%	$109.0646	$109.06	$109.05	$109.10
Purchase #5	$158.30	5.246%	$166.6044	$166.60	$166.60	$166.60
Purchase #6	$82.52	9.459%	$90.3256	$90.33	$90.35	$90.30
Purchase #7	$56.78	5.765%	$60.0534	$60.05	$60.05	$60.10
7 purchase totals =	$762.13		$823.7218	$823.72	$823.70	$823.80