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	$18.54	6.296%	$19.7073	$19.71	$19.70	$19.70
Purchase #2	$114.72	8.572%	$124.5538	$124.55	$124.55	$124.60
Purchase #3	$20.61	4.765%	$21.5921	$21.59	$21.60	$21.60
Purchase #4	$89.82	11.769%	$100.3909	$100.39	$100.40	$100.40
Purchase #5	$250.30	6.841%	$267.423	$267.42	$267.40	$267.40
Purchase #6	$58.83	6.432%	$62.6139	$62.61	$62.60	$62.60
Purchase #7	$183.63	3.430%	$189.9285	$189.93	$189.95	$189.90
7 purchase totals =	$736.45		$786.2095	$786.20	$786.20	$786.20