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	$52.52	7.344%	$56.3771	$56.38	$56.40	$56.40
Purchase #2	$184.30	10.470%	$203.5962	$203.60	$203.60	$203.60
Purchase #3	$94.57	11.254%	$105.2129	$105.21	$105.20	$105.20
Purchase #4	$96.83	4.734%	$101.4139	$101.41	$101.40	$101.40
Purchase #5	$36.25	7.411%	$38.9365	$38.94	$38.95	$38.90
Purchase #6	$86.75	4.443%	$90.6043	$90.60	$90.60	$90.60
Purchase #7	$53.52	11.469%	$59.6582	$59.66	$59.65	$59.70
7 purchase totals =	$604.74		$655.7991	$655.80	$655.80	$655.80