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	$56.53	7.707%	$60.8868	$60.89	$60.90	$60.90
Purchase #2	$112.47	5.453%	$118.603	$118.60	$118.60	$118.60
Purchase #3	$156.60	10.814%	$173.5347	$173.53	$173.55	$173.50
Purchase #4	$88.87	10.571%	$98.2644	$98.26	$98.25	$98.30
Purchase #5	$180.87	8.764%	$196.7214	$196.72	$196.70	$196.70
Purchase #6	$70.67	13.833%	$80.4458	$80.45	$80.45	$80.40
Purchase #7	$96.83	13.666%	$110.0628	$110.06	$110.05	$110.10
7 purchase totals =	$762.84		$838.5189	$838.51	$838.50	$838.50