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	$86.85	13.780%	$98.8179	$98.82	$98.80	$98.80
Purchase #2	$45.58	5.164%	$47.9338	$47.93	$47.95	$47.90
Purchase #3	$19.78	7.650%	$21.2932	$21.29	$21.30	$21.30
Purchase #4	$184.78	4.772%	$193.5977	$193.60	$193.60	$193.60
Purchase #5	$87.92	13.539%	$99.8235	$99.82	$99.80	$99.80
Purchase #6	$82.58	9.380%	$90.326	$90.33	$90.35	$90.30
Purchase #7	$99.42	13.279%	$112.622	$112.62	$112.60	$112.60
7 purchase totals =	$606.91		$664.4141	$664.41	$664.40	$664.30