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	$185.90	6.720%	$198.3925	$198.39	$198.40	$198.40
Purchase #2	$221.32	8.859%	$240.9267	$240.93	$240.95	$240.90
Purchase #3	$112.91	5.809%	$119.4689	$119.47	$119.45	$119.50
Purchase #4	$166.84	12.588%	$187.8418	$187.84	$187.85	$187.80
Purchase #5	$88.78	13.229%	$100.5247	$100.52	$100.50	$100.50
Purchase #6	$144.28	9.751%	$158.3487	$158.35	$158.35	$158.30
Purchase #7	$237.60	13.173%	$268.899	$268.90	$268.90	$268.90
7 purchase totals =	$1,157.63		$1,274.4023	$1,274.40	$1,274.40	$1,274.30