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	$93.48	3.144%	$96.419	$96.42	$96.40	$96.40
Purchase #2	$101.69	10.540%	$112.4081	$112.41	$112.40	$112.40
Purchase #3	$12.90	3.352%	$13.3324	$13.33	$13.35	$13.30
Purchase #4	$47.29	9.542%	$51.8024	$51.80	$51.80	$51.80
Purchase #5	$175.80	5.198%	$184.9381	$184.94	$184.95	$184.90
Purchase #6	$130.89	7.613%	$140.8547	$140.85	$140.85	$140.90
Purchase #7	$63.78	6.845%	$68.1457	$68.15	$68.15	$68.10
7 purchase totals =	$625.83		$667.9004	$667.90	$667.90	$667.80