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	$250.76	13.655%	$285.0013	$285.00	$285.00	$285.00
Purchase #2	$82.60	11.463%	$92.0684	$92.07	$92.05	$92.10
Purchase #3	$143.82	3.123%	$148.3115	$148.31	$148.30	$148.30
Purchase #4	$167.71	11.708%	$187.3455	$187.35	$187.35	$187.30
Purchase #5	$162.50	10.268%	$179.1855	$179.19	$179.20	$179.20
Purchase #6	$52.43	7.616%	$56.4231	$56.42	$56.40	$56.40
Purchase #7	$98.31	4.748%	$102.9778	$102.98	$103.00	$103.00
7 purchase totals =	$958.13		$1,051.3131	$1,051.32	$1,051.30	$1,051.30