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	$20.51	12.793%	$23.1338	$23.13	$23.15	$23.10
Purchase #2	$55.38	7.848%	$59.7262	$59.73	$59.75	$59.70
Purchase #3	$28.95	7.601%	$31.1505	$31.15	$31.15	$31.20
Purchase #4	$215.94	3.180%	$222.8069	$222.81	$222.80	$222.80
Purchase #5	$158.75	6.423%	$168.9465	$168.95	$168.95	$168.90
Purchase #6	$205.60	13.316%	$232.9777	$232.98	$233.00	$233.00
Purchase #7	$52.44	13.490%	$59.5142	$59.51	$59.50	$59.50
7 purchase totals =	$737.57		$798.2558	$798.26	$798.30	$798.20