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	$71.51	10.290%	$78.8684	$78.87	$78.85	$78.90
Purchase #2	$232.48	11.510%	$259.2384	$259.24	$259.25	$259.20
Purchase #3	$17.88	4.771%	$18.7331	$18.73	$18.75	$18.70
Purchase #4	$243.27	8.329%	$263.532	$263.53	$263.55	$263.50
Purchase #5	$92.87	11.562%	$103.6076	$103.61	$103.60	$103.60
Purchase #6	$194.34	10.250%	$214.2599	$214.26	$214.25	$214.30
Purchase #7	$29.80	5.163%	$31.3386	$31.34	$31.35	$31.30
7 purchase totals =	$882.15		$969.5780	$969.58	$969.60	$969.50