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	$18.29	10.211%	$20.1576	$20.16	$20.15	$20.20
Purchase #2	$42.40	8.848%	$46.1516	$46.15	$46.15	$46.20
Purchase #3	$22.91	8.750%	$24.9146	$24.91	$24.90	$24.90
Purchase #4	$227.51	12.166%	$255.1889	$255.19	$255.20	$255.20
Purchase #5	$49.57	12.497%	$55.7648	$55.76	$55.75	$55.80
Purchase #6	$119.61	7.373%	$128.4288	$128.43	$128.45	$128.40
Purchase #7	$43.50	7.812%	$46.8982	$46.90	$46.90	$46.90
7 purchase totals =	$523.79		$577.5045	$577.50	$577.50	$577.60