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	$44.52	6.683%	$47.4953	$47.50	$47.50	$47.50
Purchase #2	$137.40	11.546%	$153.2642	$153.26	$153.25	$153.30
Purchase #3	$63.77	12.361%	$71.6526	$71.65	$71.65	$71.70
Purchase #4	$98.29	13.372%	$111.4333	$111.43	$111.45	$111.40
Purchase #5	$131.46	10.367%	$145.0885	$145.09	$145.10	$145.10
Purchase #6	$171.68	11.254%	$191.0009	$191.00	$191.00	$191.00
Purchase #7	$92.34	10.461%	$101.9997	$102.00	$102.00	$102.00
7 purchase totals =	$739.46		$821.9345	$821.93	$821.95	$822.00