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	$53.82	12.368%	$60.4765	$60.48	$60.50	$60.50
Purchase #2	$57.98	4.450%	$60.5601	$60.56	$60.55	$60.60
Purchase #3	$178.49	5.739%	$188.7335	$188.73	$188.75	$188.70
Purchase #4	$80.86	10.295%	$89.1845	$89.18	$89.20	$89.20
Purchase #5	$105.94	9.806%	$116.3285	$116.33	$116.35	$116.30
Purchase #6	$159.73	11.774%	$178.5366	$178.54	$178.55	$178.50
Purchase #7	$130.79	5.177%	$137.561	$137.56	$137.55	$137.60
7 purchase totals =	$767.61		$831.3807	$831.38	$831.45	$831.40