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	$235.87	6.548%	$251.3148	$251.31	$251.30	$251.30
Purchase #2	$74.94	13.554%	$85.0974	$85.10	$85.10	$85.10
Purchase #3	$65.84	13.656%	$74.8311	$74.83	$74.85	$74.80
Purchase #4	$54.30	8.701%	$59.0246	$59.02	$59.00	$59.00
Purchase #5	$72.32	8.402%	$78.3963	$78.40	$78.40	$78.40
Purchase #6	$99.57	9.783%	$109.3109	$109.31	$109.30	$109.30
Purchase #7	$28.97	5.619%	$30.5978	$30.60	$30.60	$30.60
7 purchase totals =	$631.81		$688.5729	$688.57	$688.55	$688.50