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	$167.96	6.147%	$178.2845	$178.28	$178.30	$178.30
Purchase #2	$233.98	11.868%	$261.7487	$261.75	$261.75	$261.70
Purchase #3	$109.48	12.762%	$123.4518	$123.45	$123.45	$123.50
Purchase #4	$79.90	10.749%	$88.4885	$88.49	$88.50	$88.50
Purchase #5	$175.67	10.719%	$194.5001	$194.50	$194.50	$194.50
Purchase #6	$225.72	7.314%	$242.2292	$242.23	$242.25	$242.20
Purchase #7	$176.45	13.748%	$200.7083	$200.71	$200.70	$200.70
7 purchase totals =	$1,169.16		$1,289.4111	$1,289.41	$1,289.45	$1,289.40