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	$36.25	10.552%	$40.0751	$40.08	$40.10	$40.10
Purchase #2	$248.30	8.725%	$269.9642	$269.96	$269.95	$270.00
Purchase #3	$5.95	10.375%	$6.5673	$6.57	$6.55	$6.60
Purchase #4	$206.36	13.374%	$233.9586	$233.96	$233.95	$234.00
Purchase #5	$104.39	6.388%	$111.0584	$111.06	$111.05	$111.10
Purchase #6	$174.88	9.527%	$191.5408	$191.54	$191.55	$191.50
Purchase #7	$231.62	11.716%	$258.7566	$258.76	$258.75	$258.80
7 purchase totals =	$1,007.75		$1,111.9210	$1,111.93	$1,111.90	$1,112.10