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	$34.80	5.133%	$36.5863	$36.59	$36.60	$36.60
Purchase #2	$231.38	13.559%	$262.7528	$262.75	$262.75	$262.80
Purchase #3	$114.30	11.438%	$127.3736	$127.37	$127.35	$127.40
Purchase #4	$152.25	10.370%	$168.0383	$168.04	$168.05	$168.00
Purchase #5	$248.47	12.831%	$280.3512	$280.35	$280.35	$280.40
Purchase #6	$197.37	10.817%	$218.7195	$218.72	$218.70	$218.70
Purchase #7	$188.78	7.761%	$203.4312	$203.43	$203.45	$203.40
7 purchase totals =	$1,167.35		$1,297.2529	$1,297.25	$1,297.25	$1,297.30