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	$47.33	13.247%	$53.5998	$53.60	$53.60	$53.60
Purchase #2	$227.74	6.505%	$242.5545	$242.55	$242.55	$242.60
Purchase #3	$57.90	13.417%	$65.6684	$65.67	$65.65	$65.70
Purchase #4	$166.48	6.310%	$176.9849	$176.98	$177.00	$177.00
Purchase #5	$140.78	5.152%	$148.033	$148.03	$148.05	$148.00
Purchase #6	$114.32	10.659%	$126.5054	$126.51	$126.50	$126.50
Purchase #7	$179.98	3.645%	$186.5403	$186.54	$186.55	$186.50
7 purchase totals =	$934.53		$999.8863	$999.88	$999.90	$999.90