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	$45.65	12.136%	$51.1901	$51.19	$51.20	$51.20
Purchase #2	$100.77	13.139%	$114.0102	$114.01	$114.00	$114.00
Purchase #3	$171.52	11.153%	$190.6496	$190.65	$190.65	$190.60
Purchase #4	$117.88	13.616%	$133.9305	$133.93	$133.95	$133.90
Purchase #5	$161.65	12.485%	$181.832	$181.83	$181.85	$181.80
Purchase #6	$29.45	13.139%	$33.3194	$33.32	$33.30	$33.30
Purchase #7	$31.37	13.293%	$35.54	$35.54	$35.55	$35.50
7 purchase totals =	$658.29		$740.4718	$740.47	$740.50	$740.30