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	$138.98	4.718%	$145.5371	$145.54	$145.55	$145.50
Purchase #2	$49.91	11.162%	$55.481	$55.48	$55.50	$55.50
Purchase #3	$243.97	6.396%	$259.5743	$259.57	$259.55	$259.60
Purchase #4	$142.75	7.283%	$153.1465	$153.15	$153.15	$153.10
Purchase #5	$184.54	12.735%	$208.0412	$208.04	$208.05	$208.00
Purchase #6	$100.41	3.141%	$103.5639	$103.56	$103.55	$103.60
Purchase #7	$153.87	12.703%	$173.4161	$173.42	$173.40	$173.40
7 purchase totals =	$1,014.43		$1,098.7601	$1,098.76	$1,098.75	$1,098.70