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	$225.77	3.442%	$233.541	$233.54	$233.55	$233.50
Purchase #2	$106.53	12.167%	$119.4915	$119.49	$119.50	$119.50
Purchase #3	$232.33	12.114%	$260.4745	$260.47	$260.45	$260.50
Purchase #4	$144.61	8.403%	$156.7616	$156.76	$156.75	$156.80
Purchase #5	$93.67	5.286%	$98.6214	$98.62	$98.60	$98.60
Purchase #6	$33.95	11.289%	$37.7826	$37.78	$37.80	$37.80
Purchase #7	$130.85	11.790%	$146.2772	$146.28	$146.30	$146.30
7 purchase totals =	$967.71		$1,052.9498	$1,052.94	$1,052.95	$1,053.00