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	$73.78	10.261%	$81.3506	$81.35	$81.35	$81.40
Purchase #2	$20.41	10.325%	$22.5173	$22.52	$22.50	$22.50
Purchase #3	$63.64	10.426%	$70.2751	$70.28	$70.30	$70.30
Purchase #4	$17.61	6.775%	$18.8031	$18.80	$18.80	$18.80
Purchase #5	$61.95	13.120%	$70.0778	$70.08	$70.10	$70.10
Purchase #6	$24.58	11.691%	$27.4536	$27.45	$27.45	$27.50
Purchase #7	$130.50	10.233%	$143.8541	$143.85	$143.85	$143.90
7 purchase totals =	$392.47		$434.3316	$434.33	$434.35	$434.50