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	$48.98	11.663%	$54.6925	$54.69	$54.70	$54.70
Purchase #2	$126.25	9.236%	$137.9105	$137.91	$137.90	$137.90
Purchase #3	$19.48	9.264%	$21.2846	$21.28	$21.30	$21.30
Purchase #4	$239.39	12.390%	$269.0504	$269.05	$269.05	$269.10
Purchase #5	$65.39	8.837%	$71.1685	$71.17	$71.15	$71.20
Purchase #6	$103.71	9.809%	$113.8829	$113.88	$113.90	$113.90
Purchase #7	$230.75	12.429%	$259.4299	$259.43	$259.45	$259.40
7 purchase totals =	$833.95		$927.4193	$927.41	$927.45	$927.50