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	$18.57	13.391%	$21.0567	$21.06	$21.05	$21.10
Purchase #2	$206.80	7.364%	$222.0288	$222.03	$222.05	$222.00
Purchase #3	$145.67	7.716%	$156.9099	$156.91	$156.90	$156.90
Purchase #4	$236.72	12.187%	$265.5691	$265.57	$265.55	$265.60
Purchase #5	$152.64	7.805%	$164.5536	$164.55	$164.55	$164.60
Purchase #6	$129.55	8.527%	$140.5967	$140.60	$140.60	$140.60
Purchase #7	$160.61	3.635%	$166.4482	$166.45	$166.45	$166.40
7 purchase totals =	$1,050.56		$1,137.1630	$1,137.17	$1,137.15	$1,137.20