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	$249.97	3.521%	$258.7714	$258.77	$258.75	$258.80
Purchase #2	$162.52	13.768%	$184.8958	$184.90	$184.90	$184.90
Purchase #3	$141.88	6.839%	$151.5832	$151.58	$151.60	$151.60
Purchase #4	$245.81	4.188%	$256.1045	$256.10	$256.10	$256.10
Purchase #5	$101.45	11.175%	$112.787	$112.79	$112.80	$112.80
Purchase #6	$171.81	7.363%	$184.4604	$184.46	$184.45	$184.50
Purchase #7	$104.34	4.505%	$109.0405	$109.04	$109.05	$109.00
7 purchase totals =	$1,177.78		$1,257.6428	$1,257.64	$1,257.65	$1,257.70