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	$16.76	6.675%	$17.8787	$17.88	$17.90	$17.90
Purchase #2	$176.38	8.558%	$191.4746	$191.47	$191.45	$191.50
Purchase #3	$64.45	4.215%	$67.1666	$67.17	$67.15	$67.20
Purchase #4	$166.60	4.564%	$174.2036	$174.20	$174.20	$174.20
Purchase #5	$37.38	3.744%	$38.7795	$38.78	$38.80	$38.80
Purchase #6	$91.90	9.339%	$100.4825	$100.48	$100.50	$100.50
Purchase #7	$33.32	3.278%	$34.4122	$34.41	$34.40	$34.40
7 purchase totals =	$586.79		$624.3977	$624.39	$624.40	$624.50