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	$41.47	4.425%	$43.305	$43.31	$43.30	$43.30
Purchase #2	$239.76	10.191%	$264.1939	$264.19	$264.20	$264.20
Purchase #3	$227.89	13.816%	$259.3753	$259.38	$259.40	$259.40
Purchase #4	$142.92	8.719%	$155.3812	$155.38	$155.40	$155.40
Purchase #5	$68.41	10.327%	$75.4747	$75.47	$75.45	$75.50
Purchase #6	$114.63	12.200%	$128.6149	$128.61	$128.60	$128.60
Purchase #7	$49.98	4.167%	$52.0627	$52.06	$52.05	$52.10
7 purchase totals =	$885.06		$978.4077	$978.40	$978.40	$978.50