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	$132.85	8.805%	$144.5474	$144.55	$144.55	$144.50
Purchase #2	$178.99	9.857%	$196.633	$196.63	$196.65	$196.60
Purchase #3	$83.52	12.756%	$94.1738	$94.17	$94.15	$94.20
Purchase #4	$129.39	8.497%	$140.3843	$140.38	$140.40	$140.40
Purchase #5	$85.38	11.860%	$95.5061	$95.51	$95.50	$95.50
Purchase #6	$40.67	3.605%	$42.1362	$42.14	$42.15	$42.10
Purchase #7	$103.66	12.545%	$116.6641	$116.66	$116.65	$116.70
7 purchase totals =	$754.46		$830.0449	$830.04	$830.05	$830.00