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	$46.40	8.535%	$50.3602	$50.36	$50.35	$50.40
Purchase #2	$38.39	4.320%	$40.0484	$40.05	$40.05	$40.00
Purchase #3	$188.35	9.623%	$206.4749	$206.47	$206.45	$206.50
Purchase #4	$55.57	7.790%	$59.8989	$59.90	$59.90	$59.90
Purchase #5	$98.34	3.524%	$101.8055	$101.81	$101.80	$101.80
Purchase #6	$190.40	12.855%	$214.8759	$214.88	$214.90	$214.90
Purchase #7	$45.43	11.342%	$50.5827	$50.58	$50.60	$50.60
7 purchase totals =	$662.88		$724.0465	$724.05	$724.05	$724.10