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	$239.86	13.613%	$272.5121	$272.51	$272.50	$272.50
Purchase #2	$34.31	11.243%	$38.1675	$38.17	$38.15	$38.20
Purchase #3	$24.59	12.255%	$27.6035	$27.60	$27.60	$27.60
Purchase #4	$164.31	4.666%	$171.9767	$171.98	$172.00	$172.00
Purchase #5	$182.83	9.645%	$200.464	$200.46	$200.45	$200.50
Purchase #6	$247.83	6.833%	$264.7642	$264.76	$264.75	$264.80
Purchase #7	$27.30	3.119%	$28.1515	$28.15	$28.15	$28.20
7 purchase totals =	$921.03		$1,003.6395	$1,003.63	$1,003.60	$1,003.80