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	$231.73	11.749%	$258.956	$258.96	$258.95	$259.00
Purchase #2	$212.92	9.577%	$233.3113	$233.31	$233.30	$233.30
Purchase #3	$126.93	3.862%	$131.832	$131.83	$131.85	$131.80
Purchase #4	$108.76	9.694%	$119.3032	$119.30	$119.30	$119.30
Purchase #5	$28.53	13.616%	$32.4146	$32.41	$32.40	$32.40
Purchase #6	$158.69	9.246%	$173.3625	$173.36	$173.35	$173.40
Purchase #7	$113.85	12.447%	$128.0209	$128.02	$128.00	$128.00
7 purchase totals =	$981.41		$1,077.2005	$1,077.19	$1,077.15	$1,077.20