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	$163.79	12.611%	$184.4456	$184.45	$184.45	$184.40
Purchase #2	$220.64	8.544%	$239.4915	$239.49	$239.50	$239.50
Purchase #3	$174.46	12.839%	$196.8589	$196.86	$196.85	$196.90
Purchase #4	$102.96	5.726%	$108.8555	$108.86	$108.85	$108.90
Purchase #5	$167.48	13.746%	$190.5018	$190.50	$190.50	$190.50
Purchase #6	$74.43	8.605%	$80.8347	$80.83	$80.85	$80.80
Purchase #7	$99.47	9.858%	$109.2758	$109.28	$109.30	$109.30
7 purchase totals =	$1,003.23		$1,110.2638	$1,110.27	$1,110.30	$1,110.30