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	$88.80	5.307%	$93.5126	$93.51	$93.50	$93.50
Purchase #2	$154.31	3.317%	$159.4285	$159.43	$159.45	$159.40
Purchase #3	$17.28	12.695%	$19.4737	$19.47	$19.45	$19.50
Purchase #4	$86.31	4.840%	$90.4874	$90.49	$90.50	$90.50
Purchase #5	$114.27	10.595%	$126.3769	$126.38	$126.40	$126.40
Purchase #6	$40.53	12.253%	$45.4961	$45.50	$45.50	$45.50
Purchase #7	$17.74	7.450%	$19.0616	$19.06	$19.05	$19.10
7 purchase totals =	$519.24		$553.8368	$553.84	$553.85	$553.90