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	$50.99	7.154%	$54.6378	$54.64	$54.65	$54.60
Purchase #2	$73.93	12.318%	$83.0367	$83.04	$83.05	$83.00
Purchase #3	$97.38	6.753%	$103.9561	$103.96	$103.95	$104.00
Purchase #4	$153.30	8.791%	$166.7766	$166.78	$166.80	$166.80
Purchase #5	$24.82	4.361%	$25.9024	$25.90	$25.90	$25.90
Purchase #6	$54.83	13.805%	$62.3993	$62.40	$62.40	$62.40
Purchase #7	$107.64	4.745%	$112.7475	$112.75	$112.75	$112.70
7 purchase totals =	$562.89		$609.4564	$609.47	$609.50	$609.40