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	$179.38	4.116%	$186.7633	$186.76	$186.75	$186.80
Purchase #2	$127.83	12.716%	$144.0849	$144.08	$144.10	$144.10
Purchase #3	$25.45	6.283%	$27.049	$27.05	$27.05	$27.00
Purchase #4	$153.93	3.298%	$159.0066	$159.01	$159.00	$159.00
Purchase #5	$75.44	9.823%	$82.8505	$82.85	$82.85	$82.90
Purchase #6	$60.79	11.113%	$67.5456	$67.55	$67.55	$67.50
Purchase #7	$25.50	12.126%	$28.5921	$28.59	$28.60	$28.60
7 purchase totals =	$648.32		$695.8920	$695.89	$695.90	$695.90