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	$38.50	3.512%	$39.8521	$39.85	$39.85	$39.90
Purchase #2	$33.88	7.244%	$36.3343	$36.33	$36.35	$36.30
Purchase #3	$33.87	10.223%	$37.3325	$37.33	$37.35	$37.30
Purchase #4	$199.47	7.445%	$214.3205	$214.32	$214.30	$214.30
Purchase #5	$153.64	12.128%	$172.2735	$172.27	$172.25	$172.30
Purchase #6	$150.72	5.165%	$158.5047	$158.50	$158.50	$158.50
Purchase #7	$26.56	12.195%	$29.799	$29.80	$29.80	$29.80
7 purchase totals =	$636.64		$688.4166	$688.40	$688.40	$688.40