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	$100.71	3.869%	$104.6065	$104.61	$104.60	$104.60
Purchase #2	$129.86	12.846%	$146.5418	$146.54	$146.55	$146.50
Purchase #3	$225.71	7.407%	$242.4283	$242.43	$242.45	$242.40
Purchase #4	$86.76	5.209%	$91.2793	$91.28	$91.30	$91.30
Purchase #5	$21.54	13.800%	$24.5125	$24.51	$24.50	$24.50
Purchase #6	$169.32	13.801%	$192.6879	$192.69	$192.70	$192.70
Purchase #7	$22.81	10.641%	$25.2372	$25.24	$25.25	$25.20
7 purchase totals =	$756.71		$827.2935	$827.30	$827.35	$827.20