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	$55.73	8.381%	$60.4007	$60.40	$60.40	$60.40
Purchase #2	$42.71	3.593%	$44.2446	$44.24	$44.25	$44.20
Purchase #3	$204.33	8.731%	$222.1701	$222.17	$222.15	$222.20
Purchase #4	$160.61	11.140%	$178.502	$178.50	$178.50	$178.50
Purchase #5	$20.57	6.451%	$21.897	$21.90	$21.90	$21.90
Purchase #6	$180.93	13.351%	$205.086	$205.09	$205.10	$205.10
Purchase #7	$53.26	3.345%	$55.0415	$55.04	$55.05	$55.00
7 purchase totals =	$718.14		$787.3419	$787.34	$787.35	$787.30