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	$93.29	11.627%	$104.1368	$104.14	$104.15	$104.10
Purchase #2	$235.29	6.516%	$250.6215	$250.62	$250.60	$250.60
Purchase #3	$240.50	6.545%	$256.2407	$256.24	$256.25	$256.20
Purchase #4	$116.42	13.668%	$132.3323	$132.33	$132.35	$132.30
Purchase #5	$194.56	6.364%	$206.9418	$206.94	$206.95	$206.90
Purchase #6	$93.82	12.826%	$105.8534	$105.85	$105.85	$105.90
Purchase #7	$177.41	5.437%	$187.0558	$187.06	$187.05	$187.10
7 purchase totals =	$1,151.29		$1,243.1823	$1,243.18	$1,243.20	$1,243.10