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	$163.49	11.255%	$181.8908	$181.89	$181.90	$181.90
Purchase #2	$144.86	10.787%	$160.486	$160.49	$160.50	$160.50
Purchase #3	$174.60	10.443%	$192.8335	$192.83	$192.85	$192.80
Purchase #4	$11.90	13.281%	$13.4804	$13.48	$13.50	$13.50
Purchase #5	$178.58	9.831%	$196.1362	$196.14	$196.15	$196.10
Purchase #6	$99.36	8.765%	$108.0689	$108.07	$108.05	$108.10
Purchase #7	$25.48	10.393%	$28.1281	$28.13	$28.15	$28.10
7 purchase totals =	$798.27		$881.0239	$881.03	$881.10	$881.00