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	$147.94	13.681%	$168.1797	$168.18	$168.20	$168.20
Purchase #2	$38.79	5.324%	$40.8552	$40.86	$40.85	$40.90
Purchase #3	$117.60	13.589%	$133.5807	$133.58	$133.60	$133.60
Purchase #4	$108.82	13.157%	$123.1374	$123.14	$123.15	$123.10
Purchase #5	$166.97	4.502%	$174.487	$174.49	$174.50	$174.50
Purchase #6	$121.94	10.553%	$134.8083	$134.81	$134.80	$134.80
Purchase #7	$49.73	8.229%	$53.8223	$53.82	$53.80	$53.80
7 purchase totals =	$751.79		$828.8706	$828.88	$828.90	$828.90