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	$25.66	7.505%	$27.5858	$27.59	$27.60	$27.60
Purchase #2	$100.68	10.471%	$111.2222	$111.22	$111.20	$111.20
Purchase #3	$233.26	12.740%	$262.9773	$262.98	$263.00	$263.00
Purchase #4	$83.63	7.500%	$89.9023	$89.90	$89.90	$89.90
Purchase #5	$80.68	6.498%	$85.9226	$85.92	$85.90	$85.90
Purchase #6	$18.54	3.219%	$19.1368	$19.14	$19.15	$19.10
Purchase #7	$243.25	9.699%	$266.8428	$266.84	$266.85	$266.80
7 purchase totals =	$785.70		$863.5898	$863.59	$863.60	$863.50