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	$30.59	4.152%	$31.8601	$31.86	$31.85	$31.90
Purchase #2	$104.44	10.307%	$115.2046	$115.20	$115.20	$115.20
Purchase #3	$99.88	4.451%	$104.3257	$104.33	$104.35	$104.30
Purchase #4	$164.80	11.337%	$183.4834	$183.48	$183.50	$183.50
Purchase #5	$145.60	4.533%	$152.2	$152.20	$152.20	$152.20
Purchase #6	$93.67	10.573%	$103.5737	$103.57	$103.55	$103.60
Purchase #7	$177.85	4.705%	$186.2178	$186.22	$186.20	$186.20
7 purchase totals =	$816.83		$876.8653	$876.86	$876.85	$876.90