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	$192.56	12.409%	$216.4548	$216.45	$216.45	$216.50
Purchase #2	$21.56	13.429%	$24.4553	$24.46	$24.45	$24.50
Purchase #3	$74.94	5.163%	$78.8092	$78.81	$78.80	$78.80
Purchase #4	$14.37	13.497%	$16.3095	$16.31	$16.30	$16.30
Purchase #5	$169.96	5.275%	$178.9254	$178.93	$178.95	$178.90
Purchase #6	$32.96	13.839%	$37.5213	$37.52	$37.50	$37.50
Purchase #7	$111.90	7.800%	$120.6282	$120.63	$120.65	$120.60
7 purchase totals =	$618.25		$673.1037	$673.11	$673.10	$673.10