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	$149.38	12.720%	$168.3811	$168.38	$168.40	$168.40
Purchase #2	$191.59	6.200%	$203.4686	$203.47	$203.45	$203.50
Purchase #3	$117.44	9.377%	$128.4523	$128.45	$128.45	$128.50
Purchase #4	$40.69	7.291%	$43.6567	$43.66	$43.65	$43.70
Purchase #5	$130.60	6.354%	$138.8983	$138.90	$138.90	$138.90
Purchase #6	$186.43	3.326%	$192.6307	$192.63	$192.65	$192.60
Purchase #7	$169.44	9.717%	$185.9045	$185.90	$185.90	$185.90
7 purchase totals =	$985.57		$1,061.3922	$1,061.39	$1,061.40	$1,061.50