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	$37.31	7.781%	$40.2131	$40.21	$40.20	$40.20
Purchase #2	$217.52	5.654%	$229.8186	$229.82	$229.80	$229.80
Purchase #3	$117.83	4.148%	$122.7176	$122.72	$122.70	$122.70
Purchase #4	$36.77	5.688%	$38.8615	$38.86	$38.85	$38.90
Purchase #5	$203.59	8.169%	$220.2213	$220.22	$220.20	$220.20
Purchase #6	$208.37	6.766%	$222.4683	$222.47	$222.45	$222.50
Purchase #7	$219.57	4.232%	$228.8622	$228.86	$228.85	$228.90
7 purchase totals =	$1,040.96		$1,103.1626	$1,103.16	$1,103.05	$1,103.20