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	$25.48	9.172%	$27.817	$27.82	$27.80	$27.80
Purchase #2	$11.43	8.250%	$12.373	$12.37	$12.35	$12.40
Purchase #3	$18.86	8.606%	$20.4831	$20.48	$20.50	$20.50
Purchase #4	$152.32	13.380%	$172.7004	$172.70	$172.70	$172.70
Purchase #5	$243.55	5.112%	$256.0003	$256.00	$256.00	$256.00
Purchase #6	$100.97	13.815%	$114.919	$114.92	$114.90	$114.90
Purchase #7	$25.26	13.187%	$28.591	$28.59	$28.60	$28.60
7 purchase totals =	$577.87		$632.8838	$632.88	$632.85	$632.90