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	$89.49	6.732%	$95.5145	$95.51	$95.50	$95.50
Purchase #2	$40.72	6.858%	$43.5126	$43.51	$43.50	$43.50
Purchase #3	$223.47	13.743%	$254.1815	$254.18	$254.20	$254.20
Purchase #4	$82.26	8.204%	$89.0086	$89.01	$89.00	$89.00
Purchase #5	$128.59	12.409%	$144.5467	$144.55	$144.55	$144.50
Purchase #6	$148.96	6.770%	$159.0446	$159.04	$159.05	$159.00
Purchase #7	$77.45	6.809%	$82.7236	$82.72	$82.70	$82.70
7 purchase totals =	$790.94		$868.5321	$868.52	$868.50	$868.40