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	$93.78	11.292%	$104.3696	$104.37	$104.35	$104.40
Purchase #2	$131.71	5.749%	$139.282	$139.28	$139.30	$139.30
Purchase #3	$47.90	11.294%	$53.3098	$53.31	$53.30	$53.30
Purchase #4	$92.48	7.716%	$99.6158	$99.62	$99.60	$99.60
Purchase #5	$92.64	8.405%	$100.4264	$100.43	$100.45	$100.40
Purchase #6	$117.36	7.531%	$126.1984	$126.20	$126.20	$126.20
Purchase #7	$103.55	12.749%	$116.7516	$116.75	$116.75	$116.80
7 purchase totals =	$679.42		$739.9536	$739.96	$739.95	$740.00