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	$154.69	7.814%	$166.7775	$166.78	$166.80	$166.80
Purchase #2	$156.75	11.240%	$174.3687	$174.37	$174.35	$174.40
Purchase #3	$237.70	7.505%	$255.5394	$255.54	$255.55	$255.50
Purchase #4	$151.68	13.147%	$171.6214	$171.62	$171.60	$171.60
Purchase #5	$66.28	9.389%	$72.503	$72.50	$72.50	$72.50
Purchase #6	$199.84	8.431%	$216.6885	$216.69	$216.70	$216.70
Purchase #7	$225.53	8.657%	$245.0541	$245.05	$245.05	$245.10
7 purchase totals =	$1,192.47		$1,302.5526	$1,302.55	$1,302.55	$1,302.60