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	$186.75	11.182%	$207.6324	$207.63	$207.65	$207.60
Purchase #2	$162.97	13.810%	$185.4762	$185.48	$185.50	$185.50
Purchase #3	$126.87	7.676%	$136.6085	$136.61	$136.60	$136.60
Purchase #4	$115.42	10.295%	$127.3025	$127.30	$127.30	$127.30
Purchase #5	$250.76	11.817%	$280.3923	$280.39	$280.40	$280.40
Purchase #6	$157.41	5.486%	$166.0455	$166.05	$166.05	$166.00
Purchase #7	$15.94	13.643%	$18.1147	$18.11	$18.10	$18.10
7 purchase totals =	$1,016.12		$1,121.5721	$1,121.57	$1,121.60	$1,121.50