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	$91.38	8.726%	$99.3538	$99.35	$99.35	$99.40
Purchase #2	$186.35	11.690%	$208.1343	$208.13	$208.15	$208.10
Purchase #3	$169.56	6.146%	$179.9812	$179.98	$180.00	$180.00
Purchase #4	$217.68	4.253%	$226.9379	$226.94	$226.95	$226.90
Purchase #5	$105.58	5.465%	$111.3499	$111.35	$111.35	$111.30
Purchase #6	$237.52	5.450%	$250.4648	$250.46	$250.45	$250.50
Purchase #7	$35.55	3.424%	$36.7672	$36.77	$36.75	$36.80
7 purchase totals =	$1,043.62		$1,112.9891	$1,112.98	$1,113.00	$1,113.00