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	$25.82	10.385%	$28.5014	$28.50	$28.50	$28.50
Purchase #2	$206.87	10.187%	$227.9438	$227.94	$227.95	$227.90
Purchase #3	$132.85	8.692%	$144.3973	$144.40	$144.40	$144.40
Purchase #4	$163.92	10.722%	$181.4955	$181.50	$181.50	$181.50
Purchase #5	$107.67	8.160%	$116.4559	$116.46	$116.45	$116.50
Purchase #6	$234.53	7.250%	$251.5334	$251.53	$251.55	$251.50
Purchase #7	$61.98	11.566%	$69.1486	$69.15	$69.15	$69.10
7 purchase totals =	$933.64		$1,019.4759	$1,019.48	$1,019.50	$1,019.40