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	$173.97	7.175%	$186.4523	$186.45	$186.45	$186.50
Purchase #2	$105.40	4.236%	$109.8647	$109.86	$109.85	$109.90
Purchase #3	$148.75	8.359%	$161.184	$161.18	$161.20	$161.20
Purchase #4	$37.47	12.308%	$42.0818	$42.08	$42.10	$42.10
Purchase #5	$128.46	10.131%	$141.4743	$141.47	$141.45	$141.50
Purchase #6	$54.46	3.517%	$56.3754	$56.38	$56.40	$56.40
Purchase #7	$106.47	5.846%	$112.6942	$112.69	$112.70	$112.70
7 purchase totals =	$754.98		$810.1267	$810.11	$810.15	$810.30