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	$24.46	13.546%	$27.7734	$27.77	$27.75	$27.80
Purchase #2	$114.77	10.254%	$126.5385	$126.54	$126.55	$126.50
Purchase #3	$217.93	12.450%	$245.0623	$245.06	$245.05	$245.10
Purchase #4	$65.49	10.653%	$72.4666	$72.47	$72.45	$72.50
Purchase #5	$90.97	7.375%	$97.679	$97.68	$97.70	$97.70
Purchase #6	$100.88	10.170%	$111.1395	$111.14	$111.15	$111.10
Purchase #7	$70.79	11.808%	$79.1489	$79.15	$79.15	$79.10
7 purchase totals =	$685.29		$759.8082	$759.81	$759.80	$759.80