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	$11.80	6.350%	$12.5493	$12.55	$12.55	$12.50
Purchase #2	$104.92	12.707%	$118.2522	$118.25	$118.25	$118.30
Purchase #3	$227.98	11.306%	$253.7554	$253.76	$253.75	$253.80
Purchase #4	$57.37	9.217%	$62.6578	$62.66	$62.65	$62.70
Purchase #5	$89.77	10.796%	$99.4616	$99.46	$99.45	$99.50
Purchase #6	$207.69	13.697%	$236.1373	$236.14	$236.15	$236.10
Purchase #7	$203.76	11.167%	$226.5139	$226.51	$226.50	$226.50
7 purchase totals =	$903.29		$1,009.3275	$1,009.33	$1,009.30	$1,009.40