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	$16.62	11.270%	$18.4931	$18.49	$18.50	$18.50
Purchase #2	$114.29	11.142%	$127.0242	$127.02	$127.00	$127.00
Purchase #3	$182.62	10.818%	$202.3758	$202.38	$202.40	$202.40
Purchase #4	$233.59	9.851%	$256.601	$256.60	$256.60	$256.60
Purchase #5	$56.30	5.393%	$59.3363	$59.34	$59.35	$59.30
Purchase #6	$55.47	8.606%	$60.2437	$60.24	$60.25	$60.20
Purchase #7	$48.92	11.280%	$54.4382	$54.44	$54.45	$54.40
7 purchase totals =	$707.81		$778.5123	$778.51	$778.55	$778.40