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	$55.37	3.298%	$57.1961	$57.20	$57.20	$57.20
Purchase #2	$140.93	8.405%	$152.7752	$152.78	$152.80	$152.80
Purchase #3	$98.42	9.245%	$107.5189	$107.52	$107.50	$107.50
Purchase #4	$100.64	10.462%	$111.169	$111.17	$111.15	$111.20
Purchase #5	$49.61	8.597%	$53.875	$53.88	$53.90	$53.90
Purchase #6	$161.47	10.353%	$178.187	$178.19	$178.20	$178.20
Purchase #7	$77.43	10.611%	$85.6461	$85.65	$85.65	$85.60
7 purchase totals =	$683.87		$746.3673	$746.39	$746.40	$746.40