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	$14.78	4.418%	$15.433	$15.43	$15.45	$15.40
Purchase #2	$227.88	7.324%	$244.5699	$244.57	$244.55	$244.60
Purchase #3	$180.35	5.678%	$190.5903	$190.59	$190.60	$190.60
Purchase #4	$81.72	6.318%	$86.8831	$86.88	$86.90	$86.90
Purchase #5	$249.96	3.683%	$259.166	$259.17	$259.15	$259.20
Purchase #6	$64.28	12.766%	$72.486	$72.49	$72.50	$72.50
Purchase #7	$131.93	10.625%	$145.9476	$145.95	$145.95	$145.90
7 purchase totals =	$950.90		$1,015.0759	$1,015.08	$1,015.10	$1,015.10