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	$248.54	8.569%	$269.8374	$269.84	$269.85	$269.80
Purchase #2	$90.61	13.219%	$102.5877	$102.59	$102.60	$102.60
Purchase #3	$214.54	11.498%	$239.2078	$239.21	$239.20	$239.20
Purchase #4	$121.88	4.290%	$127.1087	$127.11	$127.10	$127.10
Purchase #5	$174.40	4.313%	$181.9219	$181.92	$181.90	$181.90
Purchase #6	$38.54	5.853%	$40.7957	$40.80	$40.80	$40.80
Purchase #7	$123.64	12.235%	$138.7674	$138.77	$138.75	$138.80
7 purchase totals =	$1,012.15		$1,100.2266	$1,100.24	$1,100.20	$1,100.20