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	$38.93	12.102%	$43.6413	$43.64	$43.65	$43.60
Purchase #2	$123.96	7.435%	$133.1764	$133.18	$133.20	$133.20
Purchase #3	$46.94	8.156%	$50.7684	$50.77	$50.75	$50.80
Purchase #4	$140.40	11.767%	$156.9209	$156.92	$156.90	$156.90
Purchase #5	$63.51	4.782%	$66.547	$66.55	$66.55	$66.50
Purchase #6	$64.59	3.750%	$67.0121	$67.01	$67.00	$67.00
Purchase #7	$141.62	5.673%	$149.6541	$149.65	$149.65	$149.70
7 purchase totals =	$619.95		$667.7202	$667.72	$667.70	$667.70