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	$236.98	8.857%	$257.9693	$257.97	$257.95	$258.00
Purchase #2	$144.90	7.112%	$155.2053	$155.21	$155.20	$155.20
Purchase #3	$127.78	10.646%	$141.3835	$141.38	$141.40	$141.40
Purchase #4	$93.61	7.460%	$100.5933	$100.59	$100.60	$100.60
Purchase #5	$45.29	12.316%	$50.8679	$50.87	$50.85	$50.90
Purchase #6	$184.82	6.570%	$196.9627	$196.96	$196.95	$197.00
Purchase #7	$143.67	3.354%	$148.4887	$148.49	$148.50	$148.50
7 purchase totals =	$977.05		$1,051.4707	$1,051.47	$1,051.45	$1,051.60