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	$104.41	13.592%	$118.6014	$118.60	$118.60	$118.60
Purchase #2	$37.37	6.581%	$39.8293	$39.83	$39.85	$39.80
Purchase #3	$23.73	8.338%	$25.7086	$25.71	$25.70	$25.70
Purchase #4	$80.33	12.773%	$90.5906	$90.59	$90.60	$90.60
Purchase #5	$144.55	12.209%	$162.1981	$162.20	$162.20	$162.20
Purchase #6	$107.59	13.658%	$122.2846	$122.28	$122.30	$122.30
Purchase #7	$90.76	5.414%	$95.6737	$95.67	$95.65	$95.70
7 purchase totals =	$588.74		$654.8863	$654.88	$654.90	$654.90