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	$25.83	7.211%	$27.6926	$27.69	$27.70	$27.70
Purchase #2	$203.61	5.861%	$215.5436	$215.54	$215.55	$215.50
Purchase #3	$212.54	13.649%	$241.5496	$241.55	$241.55	$241.50
Purchase #4	$170.84	9.237%	$186.6205	$186.62	$186.60	$186.60
Purchase #5	$157.91	7.435%	$169.6506	$169.65	$169.65	$169.70
Purchase #6	$54.48	12.244%	$61.1505	$61.15	$61.15	$61.20
Purchase #7	$103.46	7.749%	$111.4771	$111.48	$111.50	$111.50
7 purchase totals =	$928.67		$1,013.6845	$1,013.68	$1,013.70	$1,013.70