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	$158.87	12.786%	$179.1831	$179.18	$179.20	$179.20
Purchase #2	$74.56	10.388%	$82.3053	$82.31	$82.30	$82.30
Purchase #3	$17.94	5.529%	$18.9319	$18.93	$18.95	$18.90
Purchase #4	$248.32	4.172%	$258.6799	$258.68	$258.70	$258.70
Purchase #5	$81.77	8.732%	$88.9102	$88.91	$88.90	$88.90
Purchase #6	$28.76	7.397%	$30.8874	$30.89	$30.90	$30.90
Purchase #7	$79.88	13.431%	$90.6087	$90.61	$90.60	$90.60
7 purchase totals =	$690.10		$749.5065	$749.51	$749.55	$749.50