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	$39.97	6.792%	$42.6848	$42.68	$42.70	$42.70
Purchase #2	$113.61	12.626%	$127.9544	$127.95	$127.95	$128.00
Purchase #3	$214.26	4.756%	$224.4502	$224.45	$224.45	$224.50
Purchase #4	$32.49	13.468%	$36.8658	$36.87	$36.85	$36.90
Purchase #5	$166.41	13.470%	$188.8254	$188.83	$188.85	$188.80
Purchase #6	$207.96	13.605%	$236.253	$236.25	$236.25	$236.30
Purchase #7	$116.51	4.334%	$121.5595	$121.56	$121.55	$121.60
7 purchase totals =	$891.21		$978.5931	$978.59	$978.60	$978.80