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	$46.99	7.314%	$50.4268	$50.43	$50.45	$50.40
Purchase #2	$117.37	11.730%	$131.1375	$131.14	$131.15	$131.10
Purchase #3	$173.47	10.102%	$190.9939	$190.99	$191.00	$191.00
Purchase #4	$111.88	10.413%	$123.5301	$123.53	$123.55	$123.50
Purchase #5	$33.56	13.176%	$37.9819	$37.98	$38.00	$38.00
Purchase #6	$171.72	7.752%	$185.0317	$185.03	$185.05	$185.00
Purchase #7	$176.78	7.441%	$189.9342	$189.93	$189.95	$189.90
7 purchase totals =	$831.77		$909.0361	$909.03	$909.15	$908.90