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	$166.98	13.169%	$188.9696	$188.97	$188.95	$189.00
Purchase #2	$103.55	12.443%	$116.4347	$116.43	$116.45	$116.40
Purchase #3	$167.50	11.410%	$186.6118	$186.61	$186.60	$186.60
Purchase #4	$158.40	5.522%	$167.1468	$167.15	$167.15	$167.10
Purchase #5	$204.43	11.457%	$227.8515	$227.85	$227.85	$227.90
Purchase #6	$242.42	6.618%	$258.4634	$258.46	$258.45	$258.50
Purchase #7	$204.45	8.711%	$222.2596	$222.26	$222.25	$222.30
7 purchase totals =	$1,247.73		$1,367.7374	$1,367.73	$1,367.70	$1,367.80