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	$103.50	5.491%	$109.1832	$109.18	$109.20	$109.20
Purchase #2	$231.44	10.115%	$254.8502	$254.85	$254.85	$254.90
Purchase #3	$83.36	8.491%	$90.4381	$90.44	$90.45	$90.40
Purchase #4	$134.97	13.854%	$153.6687	$153.67	$153.65	$153.70
Purchase #5	$6.32	6.200%	$6.7118	$6.71	$6.70	$6.70
Purchase #6	$31.27	5.750%	$33.068	$33.07	$33.05	$33.10
Purchase #7	$119.78	7.354%	$128.5886	$128.59	$128.60	$128.60
7 purchase totals =	$710.64		$776.5086	$776.51	$776.50	$776.60