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	$26.35	10.506%	$29.1183	$29.12	$29.10	$29.10
Purchase #2	$182.61	7.397%	$196.1177	$196.12	$196.10	$196.10
Purchase #3	$58.90	13.229%	$66.6919	$66.69	$66.70	$66.70
Purchase #4	$224.59	6.864%	$240.0059	$240.01	$240.00	$240.00
Purchase #5	$249.29	9.137%	$272.0676	$272.07	$272.05	$272.10
Purchase #6	$243.76	11.527%	$271.8582	$271.86	$271.85	$271.90
Purchase #7	$62.80	12.774%	$70.8221	$70.82	$70.80	$70.80
7 purchase totals =	$1,048.30		$1,146.6817	$1,146.69	$1,146.60	$1,146.70