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	$57.72	11.694%	$64.4698	$64.47	$64.45	$64.50
Purchase #2	$158.41	10.203%	$174.5726	$174.57	$174.55	$174.60
Purchase #3	$16.92	3.415%	$17.4978	$17.50	$17.50	$17.50
Purchase #4	$106.52	7.633%	$114.6507	$114.65	$114.65	$114.70
Purchase #5	$179.45	6.206%	$190.5867	$190.59	$190.60	$190.60
Purchase #6	$119.72	10.225%	$131.9614	$131.96	$131.95	$132.00
Purchase #7	$75.88	9.284%	$82.9247	$82.92	$82.90	$82.90
7 purchase totals =	$714.62		$776.6637	$776.66	$776.60	$776.80