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	$29.35	6.692%	$31.3141	$31.31	$31.30	$31.30
Purchase #2	$214.72	3.515%	$222.2674	$222.27	$222.25	$222.30
Purchase #3	$234.73	9.456%	$256.9261	$256.93	$256.95	$256.90
Purchase #4	$82.96	12.590%	$93.4047	$93.40	$93.40	$93.40
Purchase #5	$155.76	4.596%	$162.9187	$162.92	$162.90	$162.90
Purchase #6	$47.86	9.345%	$52.3325	$52.33	$52.35	$52.30
Purchase #7	$232.63	10.422%	$256.8747	$256.87	$256.85	$256.90
7 purchase totals =	$998.01		$1,076.0382	$1,076.03	$1,076.00	$1,076.00