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	$248.35	4.211%	$258.808	$258.81	$258.80	$258.80
Purchase #2	$167.69	10.359%	$185.061	$185.06	$185.05	$185.10
Purchase #3	$67.45	7.212%	$72.3145	$72.31	$72.30	$72.30
Purchase #4	$13.65	8.392%	$14.7955	$14.80	$14.80	$14.80
Purchase #5	$88.26	11.763%	$98.642	$98.64	$98.65	$98.60
Purchase #6	$53.36	12.127%	$59.831	$59.83	$59.85	$59.80
Purchase #7	$136.70	9.840%	$150.1513	$150.15	$150.15	$150.20
7 purchase totals =	$775.46		$839.6033	$839.60	$839.60	$839.60