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	$239.82	6.832%	$256.2045	$256.20	$256.20	$256.20
Purchase #2	$245.32	13.565%	$278.5977	$278.60	$278.60	$278.60
Purchase #3	$65.30	10.196%	$71.958	$71.96	$71.95	$72.00
Purchase #4	$155.31	8.741%	$168.8856	$168.89	$168.90	$168.90
Purchase #5	$99.55	7.773%	$107.288	$107.29	$107.30	$107.30
Purchase #6	$42.98	13.766%	$48.8966	$48.90	$48.90	$48.90
Purchase #7	$232.25	11.766%	$259.5765	$259.58	$259.60	$259.60
7 purchase totals =	$1,080.53		$1,191.4069	$1,191.42	$1,191.45	$1,191.50