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	$82.48	10.111%	$90.8196	$90.82	$90.80	$90.80
Purchase #2	$99.51	6.450%	$105.9284	$105.93	$105.95	$105.90
Purchase #3	$113.88	6.197%	$120.9371	$120.94	$120.95	$120.90
Purchase #4	$87.44	3.530%	$90.5266	$90.53	$90.55	$90.50
Purchase #5	$215.69	4.426%	$225.2364	$225.24	$225.25	$225.20
Purchase #6	$189.49	7.771%	$204.2153	$204.22	$204.20	$204.20
Purchase #7	$150.72	5.238%	$158.6147	$158.61	$158.60	$158.60
7 purchase totals =	$939.21		$996.2781	$996.29	$996.30	$996.10