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	$163.28	4.404%	$170.4709	$170.47	$170.45	$170.50
Purchase #2	$131.43	10.333%	$145.0107	$145.01	$145.00	$145.00
Purchase #3	$134.81	8.656%	$146.4792	$146.48	$146.50	$146.50
Purchase #4	$250.36	10.365%	$276.3098	$276.31	$276.30	$276.30
Purchase #5	$51.57	9.370%	$56.4021	$56.40	$56.40	$56.40
Purchase #6	$41.90	13.335%	$47.4874	$47.49	$47.50	$47.50
Purchase #7	$168.79	4.165%	$175.8201	$175.82	$175.80	$175.80
7 purchase totals =	$942.14		$1,017.9802	$1,017.98	$1,017.95	$1,018.00