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	$106.85	4.710%	$111.8826	$111.88	$111.90	$111.90
Purchase #2	$92.45	11.620%	$103.1927	$103.19	$103.20	$103.20
Purchase #3	$43.93	9.835%	$48.2505	$48.25	$48.25	$48.30
Purchase #4	$117.29	12.623%	$132.0955	$132.10	$132.10	$132.10
Purchase #5	$141.46	13.631%	$160.7424	$160.74	$160.75	$160.70
Purchase #6	$143.29	11.208%	$159.3499	$159.35	$159.35	$159.30
Purchase #7	$65.55	9.512%	$71.7851	$71.79	$71.80	$71.80
7 purchase totals =	$710.82		$787.2987	$787.30	$787.35	$787.30