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	$44.91	10.424%	$49.5914	$49.59	$49.60	$49.60
Purchase #2	$88.71	13.136%	$100.3629	$100.36	$100.35	$100.40
Purchase #3	$178.58	4.286%	$186.2339	$186.23	$186.25	$186.20
Purchase #4	$229.87	4.133%	$239.3705	$239.37	$239.35	$239.40
Purchase #5	$64.47	12.464%	$72.5055	$72.51	$72.50	$72.50
Purchase #6	$155.33	11.438%	$173.0966	$173.10	$173.10	$173.10
Purchase #7	$91.69	12.486%	$103.1384	$103.14	$103.15	$103.10
7 purchase totals =	$853.56		$924.2992	$924.30	$924.30	$924.30