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	$66.72	5.688%	$70.515	$70.52	$70.50	$70.50
Purchase #2	$110.96	7.646%	$119.444	$119.44	$119.45	$119.40
Purchase #3	$103.33	5.524%	$109.0379	$109.04	$109.05	$109.00
Purchase #4	$148.42	4.707%	$155.4061	$155.41	$155.40	$155.40
Purchase #5	$99.42	13.323%	$112.6657	$112.67	$112.65	$112.70
Purchase #6	$38.33	5.654%	$40.4972	$40.50	$40.50	$40.50
Purchase #7	$144.38	13.136%	$163.3458	$163.35	$163.35	$163.30
7 purchase totals =	$711.56		$770.9117	$770.93	$770.90	$770.80