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	$120.54	8.677%	$130.9993	$131.00	$131.00	$131.00
Purchase #2	$228.85	13.506%	$259.7585	$259.76	$259.75	$259.80
Purchase #3	$100.90	10.319%	$111.3119	$111.31	$111.30	$111.30
Purchase #4	$13.44	9.426%	$14.7069	$14.71	$14.70	$14.70
Purchase #5	$55.32	11.127%	$61.4755	$61.48	$61.50	$61.50
Purchase #6	$189.58	13.116%	$214.4453	$214.45	$214.45	$214.40
Purchase #7	$68.76	4.525%	$71.8714	$71.87	$71.85	$71.90
7 purchase totals =	$777.39		$864.5688	$864.58	$864.55	$864.60