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	$30.78	5.870%	$32.5868	$32.59	$32.60	$32.60
Purchase #2	$178.33	12.592%	$200.7853	$200.79	$200.80	$200.80
Purchase #3	$127.78	9.418%	$139.8143	$139.81	$139.80	$139.80
Purchase #4	$120.28	7.703%	$129.5452	$129.55	$129.55	$129.50
Purchase #5	$159.72	8.406%	$173.1461	$173.15	$173.15	$173.10
Purchase #6	$103.49	10.589%	$114.4486	$114.45	$114.45	$114.40
Purchase #7	$108.92	3.320%	$112.5361	$112.54	$112.55	$112.50
7 purchase totals =	$829.30		$902.8624	$902.88	$902.90	$902.70