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	$246.72	8.665%	$268.0983	$268.10	$268.10	$268.10
Purchase #2	$105.76	3.489%	$109.45	$109.45	$109.45	$109.50
Purchase #3	$207.77	5.825%	$219.8726	$219.87	$219.85	$219.90
Purchase #4	$245.94	10.780%	$272.4523	$272.45	$272.45	$272.50
Purchase #5	$116.71	3.552%	$120.8555	$120.86	$120.85	$120.90
Purchase #6	$78.76	4.300%	$82.1467	$82.15	$82.15	$82.10
Purchase #7	$172.38	3.141%	$177.7945	$177.79	$177.80	$177.80
7 purchase totals =	$1,174.04		$1,250.6699	$1,250.67	$1,250.65	$1,250.80