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	$248.35	8.583%	$269.6659	$269.67	$269.65	$269.70
Purchase #2	$30.83	4.410%	$32.1896	$32.19	$32.20	$32.20
Purchase #3	$10.31	3.690%	$10.6904	$10.69	$10.70	$10.70
Purchase #4	$149.67	4.189%	$155.9397	$155.94	$155.95	$155.90
Purchase #5	$217.54	6.427%	$231.5213	$231.52	$231.50	$231.50
Purchase #6	$166.32	9.257%	$181.7162	$181.72	$181.70	$181.70
Purchase #7	$207.94	5.188%	$218.7279	$218.73	$218.75	$218.70
7 purchase totals =	$1,030.96		$1,100.4510	$1,100.46	$1,100.45	$1,100.40