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	$137.34	9.276%	$150.0797	$150.08	$150.10	$150.10
Purchase #2	$44.69	4.248%	$46.5884	$46.59	$46.60	$46.60
Purchase #3	$72.83	6.201%	$77.3462	$77.35	$77.35	$77.30
Purchase #4	$87.34	13.254%	$98.916	$98.92	$98.90	$98.90
Purchase #5	$214.99	7.822%	$231.8065	$231.81	$231.80	$231.80
Purchase #6	$102.83	8.448%	$111.5171	$111.52	$111.50	$111.50
Purchase #7	$137.89	4.759%	$144.4522	$144.45	$144.45	$144.50
7 purchase totals =	$797.91		$860.7061	$860.72	$860.70	$860.70