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	$229.32	4.192%	$238.9331	$238.93	$238.95	$238.90
Purchase #2	$221.30	7.820%	$238.6057	$238.61	$238.60	$238.60
Purchase #3	$16.47	11.572%	$18.3759	$18.38	$18.40	$18.40
Purchase #4	$153.76	9.661%	$168.6148	$168.61	$168.60	$168.60
Purchase #5	$29.52	7.871%	$31.8435	$31.84	$31.85	$31.80
Purchase #6	$175.54	4.528%	$183.4885	$183.49	$183.50	$183.50
Purchase #7	$144.45	8.290%	$156.4249	$156.42	$156.40	$156.40
7 purchase totals =	$970.36		$1,036.2864	$1,036.28	$1,036.30	$1,036.20