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	$150.82	5.586%	$159.2448	$159.24	$159.25	$159.20
Purchase #2	$129.69	9.563%	$142.0923	$142.09	$142.10	$142.10
Purchase #3	$98.89	6.659%	$105.4751	$105.48	$105.50	$105.50
Purchase #4	$192.93	3.810%	$200.2806	$200.28	$200.30	$200.30
Purchase #5	$133.86	12.659%	$150.8053	$150.81	$150.80	$150.80
Purchase #6	$19.59	6.480%	$20.8594	$20.86	$20.85	$20.90
Purchase #7	$138.86	8.696%	$150.9353	$150.94	$150.95	$150.90
7 purchase totals =	$864.64		$929.6928	$929.70	$929.75	$929.70