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	$82.71	5.191%	$87.0035	$87.00	$87.00	$87.00
Purchase #2	$40.91	10.528%	$45.217	$45.22	$45.20	$45.20
Purchase #3	$51.73	7.481%	$55.5999	$55.60	$55.60	$55.60
Purchase #4	$36.86	12.581%	$41.4974	$41.50	$41.50	$41.50
Purchase #5	$115.97	10.171%	$127.7653	$127.77	$127.75	$127.80
Purchase #6	$209.68	4.683%	$219.4993	$219.50	$219.50	$219.50
Purchase #7	$176.65	12.360%	$198.4839	$198.48	$198.50	$198.50
7 purchase totals =	$714.51		$775.0663	$775.07	$775.05	$775.10