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	$32.30	3.605%	$33.4644	$33.46	$33.45	$33.50
Purchase #2	$26.49	10.225%	$29.1986	$29.20	$29.20	$29.20
Purchase #3	$89.75	12.326%	$100.8126	$100.81	$100.80	$100.80
Purchase #4	$207.66	13.131%	$234.9278	$234.93	$234.95	$234.90
Purchase #5	$66.95	6.276%	$71.1518	$71.15	$71.15	$71.20
Purchase #6	$142.77	3.540%	$147.8241	$147.82	$147.80	$147.80
Purchase #7	$103.71	7.392%	$111.3762	$111.38	$111.40	$111.40
7 purchase totals =	$669.63		$728.7555	$728.75	$728.75	$728.80