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	$112.82	5.810%	$119.3748	$119.37	$119.35	$119.40
Purchase #2	$84.58	6.702%	$90.2486	$90.25	$90.25	$90.20
Purchase #3	$41.50	10.462%	$45.8417	$45.84	$45.85	$45.80
Purchase #4	$50.31	12.803%	$56.7512	$56.75	$56.75	$56.80
Purchase #5	$135.55	7.279%	$145.4167	$145.42	$145.40	$145.40
Purchase #6	$241.86	10.445%	$267.1223	$267.12	$267.10	$267.10
Purchase #7	$111.66	7.139%	$119.6314	$119.63	$119.65	$119.60
7 purchase totals =	$778.28		$844.3867	$844.38	$844.35	$844.30