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	$122.74	7.294%	$131.6927	$131.69	$131.70	$131.70
Purchase #2	$180.39	5.489%	$190.2916	$190.29	$190.30	$190.30
Purchase #3	$74.72	6.261%	$79.3982	$79.40	$79.40	$79.40
Purchase #4	$82.69	8.253%	$89.5144	$89.51	$89.50	$89.50
Purchase #5	$200.40	12.844%	$226.1394	$226.14	$226.15	$226.10
Purchase #6	$66.37	10.102%	$73.0747	$73.07	$73.05	$73.10
Purchase #7	$171.32	5.523%	$180.782	$180.78	$180.80	$180.80
7 purchase totals =	$898.63		$970.8930	$970.88	$970.90	$970.90