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	$39.68	3.119%	$40.9176	$40.92	$40.90	$40.90
Purchase #2	$239.87	9.831%	$263.4516	$263.45	$263.45	$263.50
Purchase #3	$106.73	4.693%	$111.7388	$111.74	$111.75	$111.70
Purchase #4	$243.41	12.310%	$273.3738	$273.37	$273.35	$273.40
Purchase #5	$85.92	6.867%	$91.8201	$91.82	$91.80	$91.80
Purchase #6	$117.50	5.182%	$123.5889	$123.59	$123.60	$123.60
Purchase #7	$65.29	9.544%	$71.5213	$71.52	$71.50	$71.50
7 purchase totals =	$898.40		$976.4121	$976.41	$976.35	$976.40