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	$133.47	11.476%	$148.787	$148.79	$148.80	$148.80
Purchase #2	$111.61	12.515%	$125.578	$125.58	$125.60	$125.60
Purchase #3	$47.25	10.738%	$52.3237	$52.32	$52.30	$52.30
Purchase #4	$81.50	10.651%	$90.1806	$90.18	$90.20	$90.20
Purchase #5	$176.29	11.368%	$196.3306	$196.33	$196.35	$196.30
Purchase #6	$66.33	3.684%	$68.7736	$68.77	$68.75	$68.80
Purchase #7	$212.45	13.831%	$241.834	$241.83	$241.85	$241.80
7 purchase totals =	$828.90		$923.8075	$923.80	$923.85	$923.80