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	$174.48	8.602%	$189.4888	$189.49	$189.50	$189.50
Purchase #2	$71.57	9.839%	$78.6118	$78.61	$78.60	$78.60
Purchase #3	$152.58	10.863%	$169.1548	$169.15	$169.15	$169.20
Purchase #4	$63.59	4.244%	$66.2888	$66.29	$66.30	$66.30
Purchase #5	$175.96	6.849%	$188.0115	$188.01	$188.00	$188.00
Purchase #6	$239.78	11.587%	$267.5633	$267.56	$267.55	$267.60
Purchase #7	$92.68	10.144%	$102.0815	$102.08	$102.10	$102.10
7 purchase totals =	$970.64		$1,061.2005	$1,061.19	$1,061.20	$1,061.30