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	$226.69	6.390%	$241.1755	$241.18	$241.20	$241.20
Purchase #2	$179.60	4.167%	$187.0839	$187.08	$187.10	$187.10
Purchase #3	$91.50	7.599%	$98.4531	$98.45	$98.45	$98.50
Purchase #4	$242.65	13.643%	$275.7547	$275.75	$275.75	$275.80
Purchase #5	$169.73	11.181%	$188.7075	$188.71	$188.70	$188.70
Purchase #6	$25.45	11.161%	$28.2905	$28.29	$28.30	$28.30
Purchase #7	$63.78	12.871%	$71.9891	$71.99	$72.00	$72.00
7 purchase totals =	$999.40		$1,091.4543	$1,091.45	$1,091.50	$1,091.60