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	$186.66	7.423%	$200.5158	$200.52	$200.50	$200.50
Purchase #2	$81.80	10.714%	$90.5641	$90.56	$90.55	$90.60
Purchase #3	$51.38	11.168%	$57.1181	$57.12	$57.10	$57.10
Purchase #4	$76.29	9.221%	$83.3247	$83.32	$83.30	$83.30
Purchase #5	$50.75	10.771%	$56.2163	$56.22	$56.20	$56.20
Purchase #6	$214.27	12.590%	$241.2466	$241.25	$241.25	$241.20
Purchase #7	$122.59	6.215%	$130.209	$130.21	$130.20	$130.20
7 purchase totals =	$783.74		$859.1946	$859.20	$859.10	$859.10