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	$28.81	6.788%	$30.7656	$30.77	$30.75	$30.80
Purchase #2	$197.78	12.642%	$222.7833	$222.78	$222.80	$222.80
Purchase #3	$241.44	7.443%	$259.4104	$259.41	$259.40	$259.40
Purchase #4	$29.58	13.361%	$33.5322	$33.53	$33.55	$33.50
Purchase #5	$69.85	7.720%	$75.2424	$75.24	$75.25	$75.20
Purchase #6	$54.72	3.475%	$56.6215	$56.62	$56.60	$56.60
Purchase #7	$105.56	5.322%	$111.1779	$111.18	$111.20	$111.20
7 purchase totals =	$727.74		$789.5333	$789.53	$789.55	$789.50