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	$47.64	12.621%	$53.6526	$53.65	$53.65	$53.70
Purchase #2	$216.45	11.244%	$240.7876	$240.79	$240.80	$240.80
Purchase #3	$80.47	3.815%	$83.5399	$83.54	$83.55	$83.50
Purchase #4	$160.63	9.210%	$175.424	$175.42	$175.40	$175.40
Purchase #5	$169.87	13.168%	$192.2385	$192.24	$192.25	$192.20
Purchase #6	$101.35	9.836%	$111.3188	$111.32	$111.30	$111.30
Purchase #7	$13.51	10.833%	$14.9735	$14.97	$14.95	$15.00
7 purchase totals =	$789.92		$871.9349	$871.93	$871.90	$871.90