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	$38.45	10.619%	$42.533	$42.53	$42.55	$42.50
Purchase #2	$206.80	13.664%	$235.0572	$235.06	$235.05	$235.10
Purchase #3	$11.81	5.712%	$12.4846	$12.48	$12.50	$12.50
Purchase #4	$44.43	3.391%	$45.9366	$45.94	$45.95	$45.90
Purchase #5	$52.26	4.474%	$54.5981	$54.60	$54.60	$54.60
Purchase #6	$139.74	8.812%	$152.0539	$152.05	$152.05	$152.10
Purchase #7	$56.63	7.337%	$60.7849	$60.78	$60.80	$60.80
7 purchase totals =	$550.12		$603.4483	$603.44	$603.50	$603.50