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	$162.86	3.732%	$168.9379	$168.94	$168.95	$168.90
Purchase #2	$60.83	10.259%	$67.0705	$67.07	$67.05	$67.10
Purchase #3	$128.68	4.874%	$134.9519	$134.95	$134.95	$135.00
Purchase #4	$250.96	8.215%	$271.5764	$271.58	$271.60	$271.60
Purchase #5	$141.77	4.525%	$148.1851	$148.19	$148.20	$148.20
Purchase #6	$72.84	7.407%	$78.2353	$78.24	$78.25	$78.20
Purchase #7	$73.88	13.357%	$83.7482	$83.75	$83.75	$83.70
7 purchase totals =	$891.82		$952.7053	$952.72	$952.75	$952.70