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	$138.86	8.256%	$150.3243	$150.32	$150.30	$150.30
Purchase #2	$118.92	12.783%	$134.1215	$134.12	$134.10	$134.10
Purchase #3	$28.39	7.585%	$30.5434	$30.54	$30.55	$30.50
Purchase #4	$39.38	10.426%	$43.4858	$43.49	$43.50	$43.50
Purchase #5	$60.93	11.157%	$67.728	$67.73	$67.75	$67.70
Purchase #6	$7.32	3.645%	$7.5868	$7.59	$7.60	$7.60
Purchase #7	$200.93	5.208%	$211.3944	$211.39	$211.40	$211.40
7 purchase totals =	$594.73		$645.1842	$645.18	$645.20	$645.10