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	$200.72	10.789%	$222.3757	$222.38	$222.40	$222.40
Purchase #2	$10.76	9.262%	$11.7566	$11.76	$11.75	$11.80
Purchase #3	$44.95	9.507%	$49.2234	$49.22	$49.20	$49.20
Purchase #4	$43.94	3.256%	$45.3707	$45.37	$45.35	$45.40
Purchase #5	$107.43	13.482%	$121.9137	$121.91	$121.90	$121.90
Purchase #6	$220.96	13.279%	$250.3013	$250.30	$250.30	$250.30
Purchase #7	$113.70	4.863%	$119.2292	$119.23	$119.25	$119.20
7 purchase totals =	$742.46		$820.1706	$820.17	$820.15	$820.20