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	$123.39	4.400%	$128.8192	$128.82	$128.80	$128.80
Purchase #2	$63.94	3.184%	$65.9758	$65.98	$66.00	$66.00
Purchase #3	$45.39	4.252%	$47.32	$47.32	$47.30	$47.30
Purchase #4	$146.33	13.357%	$165.8753	$165.88	$165.90	$165.90
Purchase #5	$65.90	3.592%	$68.2671	$68.27	$68.25	$68.30
Purchase #6	$24.78	9.856%	$27.2223	$27.22	$27.20	$27.20
Purchase #7	$172.83	5.805%	$182.8628	$182.86	$182.85	$182.90
7 purchase totals =	$642.56		$686.3425	$686.35	$686.30	$686.40