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	$72.47	13.776%	$82.4535	$82.45	$82.45	$82.50
Purchase #2	$50.69	5.624%	$53.5408	$53.54	$53.55	$53.50
Purchase #3	$161.30	7.730%	$173.7685	$173.77	$173.75	$173.80
Purchase #4	$134.98	3.411%	$139.5842	$139.58	$139.60	$139.60
Purchase #5	$61.44	9.188%	$67.0851	$67.09	$67.10	$67.10
Purchase #6	$158.60	6.449%	$168.8281	$168.83	$168.85	$168.80
Purchase #7	$125.25	8.211%	$135.5343	$135.53	$135.55	$135.50
7 purchase totals =	$764.73		$820.7945	$820.79	$820.85	$820.80