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	$236.27	12.258%	$265.232	$265.23	$265.25	$265.20
Purchase #2	$43.66	7.543%	$46.9533	$46.95	$46.95	$47.00
Purchase #3	$42.53	4.503%	$44.4451	$44.45	$44.45	$44.40
Purchase #4	$80.69	7.670%	$86.8789	$86.88	$86.90	$86.90
Purchase #5	$66.27	9.411%	$72.5067	$72.51	$72.50	$72.50
Purchase #6	$206.56	6.109%	$219.1788	$219.18	$219.20	$219.20
Purchase #7	$116.42	10.445%	$128.5801	$128.58	$128.60	$128.60
7 purchase totals =	$792.40		$863.7749	$863.78	$863.85	$863.80