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	$89.95	9.198%	$98.2236	$98.22	$98.20	$98.20
Purchase #2	$13.31	8.803%	$14.4817	$14.48	$14.50	$14.50
Purchase #3	$27.92	12.204%	$31.3274	$31.33	$31.35	$31.30
Purchase #4	$99.96	5.111%	$105.069	$105.07	$105.05	$105.10
Purchase #5	$76.67	13.631%	$87.1209	$87.12	$87.10	$87.10
Purchase #6	$182.57	3.855%	$189.6081	$189.61	$189.60	$189.60
Purchase #7	$250.63	11.566%	$279.6179	$279.62	$279.60	$279.60
7 purchase totals =	$741.01		$805.4486	$805.45	$805.40	$805.40