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	$143.60	8.642%	$156.0099	$156.01	$156.00	$156.00
Purchase #2	$97.36	12.488%	$109.5183	$109.52	$109.50	$109.50
Purchase #3	$215.46	10.433%	$237.9389	$237.94	$237.95	$237.90
Purchase #4	$143.43	6.700%	$153.0398	$153.04	$153.05	$153.00
Purchase #5	$24.67	12.344%	$27.7153	$27.72	$27.70	$27.70
Purchase #6	$130.50	10.679%	$144.4361	$144.44	$144.45	$144.40
Purchase #7	$101.60	11.777%	$113.5654	$113.57	$113.55	$113.60
7 purchase totals =	$856.62		$942.2237	$942.24	$942.20	$942.10