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	$21.92	13.181%	$24.8093	$24.81	$24.80	$24.80
Purchase #2	$142.61	3.557%	$147.6826	$147.68	$147.70	$147.70
Purchase #3	$234.47	10.401%	$258.8572	$258.86	$258.85	$258.90
Purchase #4	$52.34	13.865%	$59.5969	$59.60	$59.60	$59.60
Purchase #5	$197.28	6.412%	$209.9296	$209.93	$209.95	$209.90
Purchase #6	$74.84	11.301%	$83.2977	$83.30	$83.30	$83.30
Purchase #7	$165.65	11.682%	$185.0012	$185.00	$185.00	$185.00
7 purchase totals =	$889.11		$969.1745	$969.18	$969.20	$969.20