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	$98.46	6.491%	$104.851	$104.85	$104.85	$104.90
Purchase #2	$151.86	10.277%	$167.4667	$167.47	$167.45	$167.50
Purchase #3	$248.70	12.692%	$280.265	$280.27	$280.25	$280.30
Purchase #4	$46.85	11.209%	$52.1014	$52.10	$52.10	$52.10
Purchase #5	$60.78	5.290%	$63.9953	$64.00	$64.00	$64.00
Purchase #6	$110.47	3.308%	$114.1243	$114.12	$114.10	$114.10
Purchase #7	$66.73	5.107%	$70.1379	$70.14	$70.15	$70.10
7 purchase totals =	$783.85		$852.9416	$852.95	$852.90	$853.00