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	$45.90	3.422%	$47.4707	$47.47	$47.45	$47.50
Purchase #2	$165.88	3.786%	$172.1602	$172.16	$172.15	$172.20
Purchase #3	$32.70	5.824%	$34.6044	$34.60	$34.60	$34.60
Purchase #4	$9.84	6.317%	$10.4616	$10.46	$10.45	$10.50
Purchase #5	$178.43	12.202%	$200.202	$200.20	$200.20	$200.20
Purchase #6	$80.34	6.722%	$85.7405	$85.74	$85.75	$85.70
Purchase #7	$37.45	10.642%	$41.4354	$41.44	$41.45	$41.40
7 purchase totals =	$550.54		$592.0748	$592.07	$592.05	$592.10