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	$28.56	10.611%	$31.5905	$31.59	$31.60	$31.60
Purchase #2	$181.66	6.778%	$193.9729	$193.97	$193.95	$194.00
Purchase #3	$74.97	5.812%	$79.3273	$79.33	$79.35	$79.30
Purchase #4	$144.66	7.278%	$155.1884	$155.19	$155.20	$155.20
Purchase #5	$16.52	9.483%	$18.0866	$18.09	$18.10	$18.10
Purchase #6	$56.56	5.376%	$59.6007	$59.60	$59.60	$59.60
Purchase #7	$30.96	6.235%	$32.8904	$32.89	$32.90	$32.90
7 purchase totals =	$533.89		$570.6568	$570.66	$570.70	$570.70