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	$249.86	5.117%	$262.6453	$262.65	$262.65	$262.60
Purchase #2	$242.77	9.409%	$265.6122	$265.61	$265.60	$265.60
Purchase #3	$82.61	9.336%	$90.3225	$90.32	$90.30	$90.30
Purchase #4	$145.67	3.417%	$150.6475	$150.65	$150.65	$150.60
Purchase #5	$21.51	6.443%	$22.8959	$22.90	$22.90	$22.90
Purchase #6	$92.83	12.341%	$104.2862	$104.29	$104.30	$104.30
Purchase #7	$204.63	7.255%	$219.4759	$219.48	$219.50	$219.50
7 purchase totals =	$1,039.88		$1,115.8855	$1,115.90	$1,115.90	$1,115.80