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	$221.99	7.612%	$238.8879	$238.89	$238.90	$238.90
Purchase #2	$120.31	11.678%	$134.3598	$134.36	$134.35	$134.40
Purchase #3	$163.39	3.156%	$168.5466	$168.55	$168.55	$168.50
Purchase #4	$200.25	10.409%	$221.094	$221.09	$221.10	$221.10
Purchase #5	$7.40	6.436%	$7.8763	$7.88	$7.90	$7.90
Purchase #6	$17.83	12.339%	$20.03	$20.03	$20.05	$20.00
Purchase #7	$89.35	13.114%	$101.0674	$101.07	$101.05	$101.10
7 purchase totals =	$820.52		$891.8620	$891.87	$891.90	$891.90