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	$99.42	9.566%	$108.9305	$108.93	$108.95	$108.90
Purchase #2	$201.99	5.342%	$212.7803	$212.78	$212.80	$212.80
Purchase #3	$136.83	13.291%	$155.0161	$155.02	$155.00	$155.00
Purchase #4	$105.27	9.140%	$114.8917	$114.89	$114.90	$114.90
Purchase #5	$39.64	10.274%	$43.7126	$43.71	$43.70	$43.70
Purchase #6	$52.85	12.228%	$59.3125	$59.31	$59.30	$59.30
Purchase #7	$169.74	13.841%	$193.2337	$193.23	$193.25	$193.20
7 purchase totals =	$805.74		$887.8774	$887.87	$887.90	$887.80