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	$139.74	4.303%	$145.753	$145.75	$145.75	$145.80
Purchase #2	$171.44	3.146%	$176.8335	$176.83	$176.85	$176.80
Purchase #3	$92.59	8.667%	$100.6148	$100.61	$100.60	$100.60
Purchase #4	$27.55	3.504%	$28.5154	$28.52	$28.50	$28.50
Purchase #5	$20.93	10.848%	$23.2005	$23.20	$23.20	$23.20
Purchase #6	$152.65	7.806%	$164.5659	$164.57	$164.55	$164.60
Purchase #7	$102.54	9.155%	$111.9275	$111.93	$111.95	$111.90
7 purchase totals =	$707.44		$751.4106	$751.41	$751.40	$751.40