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	$166.36	10.706%	$184.1705	$184.17	$184.15	$184.20
Purchase #2	$77.99	3.757%	$80.9201	$80.92	$80.90	$80.90
Purchase #3	$27.49	7.813%	$29.6378	$29.64	$29.65	$29.60
Purchase #4	$97.99	7.297%	$105.1403	$105.14	$105.15	$105.10
Purchase #5	$39.83	12.778%	$44.9195	$44.92	$44.90	$44.90
Purchase #6	$56.25	5.852%	$59.5418	$59.54	$59.55	$59.50
Purchase #7	$174.65	4.706%	$182.869	$182.87	$182.85	$182.90
7 purchase totals =	$640.56		$687.1990	$687.20	$687.15	$687.10