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	$239.61	11.499%	$267.1628	$267.16	$267.15	$267.20
Purchase #2	$127.27	11.532%	$141.9468	$141.95	$141.95	$141.90
Purchase #3	$81.65	10.367%	$90.1147	$90.11	$90.10	$90.10
Purchase #4	$111.57	10.160%	$122.9055	$122.91	$122.90	$122.90
Purchase #5	$199.86	9.257%	$218.361	$218.36	$218.35	$218.40
Purchase #6	$44.39	6.573%	$47.3078	$47.31	$47.30	$47.30
Purchase #7	$94.42	11.684%	$105.452	$105.45	$105.45	$105.50
7 purchase totals =	$898.77		$993.2506	$993.25	$993.20	$993.30