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	$64.80	11.832%	$72.4671	$72.47	$72.45	$72.50
Purchase #2	$7.82	5.724%	$8.2676	$8.27	$8.25	$8.30
Purchase #3	$103.30	5.576%	$109.06	$109.06	$109.05	$109.10
Purchase #4	$134.35	10.494%	$148.4487	$148.45	$148.45	$148.40
Purchase #5	$116.81	9.671%	$128.1067	$128.11	$128.10	$128.10
Purchase #6	$177.54	12.489%	$199.713	$199.71	$199.70	$199.70
Purchase #7	$164.50	4.386%	$171.715	$171.72	$171.70	$171.70
7 purchase totals =	$769.12		$837.7781	$837.79	$837.70	$837.80