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	$140.83	13.468%	$159.797	$159.80	$159.80	$159.80
Purchase #2	$225.83	8.370%	$244.732	$244.73	$244.75	$244.70
Purchase #3	$29.88	6.250%	$31.7475	$31.75	$31.75	$31.70
Purchase #4	$154.59	10.695%	$171.1234	$171.12	$171.10	$171.10
Purchase #5	$100.25	6.286%	$106.5517	$106.55	$106.55	$106.60
Purchase #6	$40.72	6.434%	$43.3399	$43.34	$43.35	$43.30
Purchase #7	$137.33	3.609%	$142.2862	$142.29	$142.30	$142.30
7 purchase totals =	$829.43		$899.5777	$899.58	$899.60	$899.50