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	$137.28	8.226%	$148.5727	$148.57	$148.55	$148.60
Purchase #2	$212.79	8.167%	$230.1686	$230.17	$230.15	$230.20
Purchase #3	$123.39	6.368%	$131.2475	$131.25	$131.25	$131.20
Purchase #4	$48.81	4.660%	$51.0845	$51.08	$51.10	$51.10
Purchase #5	$33.57	11.436%	$37.4091	$37.41	$37.40	$37.40
Purchase #6	$54.54	8.213%	$59.0194	$59.02	$59.00	$59.00
Purchase #7	$191.52	12.411%	$215.2895	$215.29	$215.30	$215.30
7 purchase totals =	$801.90		$872.7913	$872.79	$872.75	$872.80