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	$9.60	4.326%	$10.0153	$10.02	$10.00	$10.00
Purchase #2	$171.47	7.590%	$184.4846	$184.48	$184.50	$184.50
Purchase #3	$9.58	8.816%	$10.4246	$10.42	$10.40	$10.40
Purchase #4	$186.41	13.821%	$212.1737	$212.17	$212.15	$212.20
Purchase #5	$187.78	13.703%	$213.5115	$213.51	$213.50	$213.50
Purchase #6	$154.39	13.284%	$174.8992	$174.90	$174.90	$174.90
Purchase #7	$18.80	8.503%	$20.3986	$20.40	$20.40	$20.40
7 purchase totals =	$738.03		$825.9075	$825.90	$825.85	$825.90