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	$46.80	13.705%	$53.2139	$53.21	$53.20	$53.20
Purchase #2	$206.92	11.856%	$231.4524	$231.45	$231.45	$231.50
Purchase #3	$110.83	9.826%	$121.7202	$121.72	$121.70	$121.70
Purchase #4	$80.96	6.742%	$86.4183	$86.42	$86.40	$86.40
Purchase #5	$134.94	4.857%	$141.494	$141.49	$141.50	$141.50
Purchase #6	$17.58	7.580%	$18.9126	$18.91	$18.90	$18.90
Purchase #7	$11.38	13.298%	$12.8933	$12.89	$12.90	$12.90
7 purchase totals =	$609.41		$666.1047	$666.09	$666.05	$666.10