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	$134.40	3.283%	$138.8124	$138.81	$138.80	$138.80
Purchase #2	$78.77	8.801%	$85.7025	$85.70	$85.70	$85.70
Purchase #3	$204.81	6.410%	$217.9383	$217.94	$217.95	$217.90
Purchase #4	$79.65	13.867%	$90.6951	$90.70	$90.70	$90.70
Purchase #5	$235.83	12.178%	$264.5494	$264.55	$264.55	$264.50
Purchase #6	$66.66	7.443%	$71.6215	$71.62	$71.60	$71.60
Purchase #7	$48.93	12.147%	$54.8735	$54.87	$54.85	$54.90
7 purchase totals =	$849.05		$924.1927	$924.19	$924.15	$924.10