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	$241.77	7.314%	$259.4531	$259.45	$259.45	$259.50
Purchase #2	$200.39	13.728%	$227.8995	$227.90	$227.90	$227.90
Purchase #3	$81.78	9.205%	$89.3078	$89.31	$89.30	$89.30
Purchase #4	$39.89	11.124%	$44.3274	$44.33	$44.35	$44.30
Purchase #5	$20.55	13.114%	$23.2449	$23.24	$23.25	$23.20
Purchase #6	$132.72	8.839%	$144.4511	$144.45	$144.45	$144.50
Purchase #7	$142.39	6.790%	$152.0583	$152.06	$152.05	$152.10
7 purchase totals =	$859.49		$940.7421	$940.74	$940.75	$940.80