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	$51.55	8.418%	$55.8895	$55.89	$55.90	$55.90
Purchase #2	$94.93	9.214%	$103.6769	$103.68	$103.70	$103.70
Purchase #3	$58.60	4.195%	$61.0583	$61.06	$61.05	$61.10
Purchase #4	$173.88	8.660%	$188.938	$188.94	$188.95	$188.90
Purchase #5	$247.28	10.527%	$273.3112	$273.31	$273.30	$273.30
Purchase #6	$57.40	4.326%	$59.8831	$59.88	$59.90	$59.90
Purchase #7	$66.64	4.591%	$69.6994	$69.70	$69.70	$69.70
7 purchase totals =	$750.28		$812.4564	$812.46	$812.50	$812.50