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	$75.47	4.763%	$79.0646	$79.06	$79.05	$79.10
Purchase #2	$217.80	6.300%	$231.5214	$231.52	$231.50	$231.50
Purchase #3	$75.26	9.791%	$82.6287	$82.63	$82.65	$82.60
Purchase #4	$225.62	12.263%	$253.2878	$253.29	$253.30	$253.30
Purchase #5	$55.46	5.641%	$58.5885	$58.59	$58.60	$58.60
Purchase #6	$78.60	5.680%	$83.0645	$83.06	$83.05	$83.10
Purchase #7	$129.89	10.183%	$143.1167	$143.12	$143.10	$143.10
7 purchase totals =	$858.10		$931.2722	$931.27	$931.25	$931.30