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	$176.72	6.149%	$187.5865	$187.59	$187.60	$187.60
Purchase #2	$237.97	10.243%	$262.3453	$262.35	$262.35	$262.30
Purchase #3	$123.81	12.408%	$139.1723	$139.17	$139.15	$139.20
Purchase #4	$19.98	6.183%	$21.2154	$21.22	$21.20	$21.20
Purchase #5	$124.96	11.288%	$139.0655	$139.07	$139.05	$139.10
Purchase #6	$240.48	12.574%	$270.718	$270.72	$270.70	$270.70
Purchase #7	$46.56	13.343%	$52.7725	$52.77	$52.75	$52.80
7 purchase totals =	$970.48		$1,072.8755	$1,072.89	$1,072.80	$1,072.90