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	$235.80	6.220%	$250.4668	$250.47	$250.45	$250.50
Purchase #2	$111.78	6.346%	$118.8736	$118.87	$118.85	$118.90
Purchase #3	$101.46	10.569%	$112.1833	$112.18	$112.20	$112.20
Purchase #4	$51.52	8.108%	$55.6972	$55.70	$55.70	$55.70
Purchase #5	$215.42	8.394%	$233.5024	$233.50	$233.50	$233.50
Purchase #6	$85.85	13.748%	$97.6527	$97.65	$97.65	$97.70
Purchase #7	$144.94	12.410%	$162.9271	$162.93	$162.95	$162.90
7 purchase totals =	$946.77		$1,031.3031	$1,031.30	$1,031.30	$1,031.40