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	$91.28	10.565%	$100.9237	$100.92	$100.90	$100.90
Purchase #2	$250.89	8.747%	$272.8353	$272.84	$272.85	$272.80
Purchase #3	$12.29	5.223%	$12.9319	$12.93	$12.95	$12.90
Purchase #4	$117.82	7.719%	$126.9145	$126.91	$126.90	$126.90
Purchase #5	$26.71	5.737%	$28.2424	$28.24	$28.25	$28.20
Purchase #6	$131.26	13.331%	$148.7583	$148.76	$148.75	$148.80
Purchase #7	$140.97	7.740%	$151.8811	$151.88	$151.90	$151.90
7 purchase totals =	$771.22		$842.4872	$842.48	$842.50	$842.40