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	$74.53	5.326%	$78.4995	$78.50	$78.50	$78.50
Purchase #2	$39.27	7.551%	$42.2353	$42.24	$42.25	$42.20
Purchase #3	$240.64	12.556%	$270.8548	$270.85	$270.85	$270.90
Purchase #4	$171.45	11.636%	$191.3999	$191.40	$191.40	$191.40
Purchase #5	$42.59	13.215%	$48.2183	$48.22	$48.20	$48.20
Purchase #6	$9.83	10.308%	$10.8433	$10.84	$10.85	$10.80
Purchase #7	$70.81	3.689%	$73.4222	$73.42	$73.40	$73.40
7 purchase totals =	$649.12		$715.4733	$715.47	$715.45	$715.40