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	$227.85	3.114%	$234.9452	$234.95	$234.95	$234.90
Purchase #2	$53.51	3.432%	$55.3465	$55.35	$55.35	$55.30
Purchase #3	$166.63	13.199%	$188.6235	$188.62	$188.60	$188.60
Purchase #4	$116.86	5.512%	$123.3013	$123.30	$123.30	$123.30
Purchase #5	$180.85	4.679%	$189.312	$189.31	$189.30	$189.30
Purchase #6	$201.64	10.815%	$223.4474	$223.45	$223.45	$223.40
Purchase #7	$50.56	9.522%	$55.3743	$55.37	$55.35	$55.40
7 purchase totals =	$997.90		$1,070.3502	$1,070.35	$1,070.30	$1,070.20