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	$113.40	12.374%	$127.4321	$127.43	$127.45	$127.40
Purchase #2	$248.88	7.127%	$266.6177	$266.62	$266.60	$266.60
Purchase #3	$16.45	9.789%	$18.0603	$18.06	$18.05	$18.10
Purchase #4	$224.25	5.518%	$236.6241	$236.62	$236.60	$236.60
Purchase #5	$138.47	13.467%	$157.1178	$157.12	$157.10	$157.10
Purchase #6	$116.59	11.193%	$129.6399	$129.64	$129.65	$129.60
Purchase #7	$59.68	12.519%	$67.1513	$67.15	$67.15	$67.20
7 purchase totals =	$917.72		$1,002.6432	$1,002.64	$1,002.60	$1,002.60