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	$159.54	6.816%	$170.4142	$170.41	$170.40	$170.40
Purchase #2	$37.92	6.732%	$40.4728	$40.47	$40.45	$40.50
Purchase #3	$83.72	5.633%	$88.4359	$88.44	$88.45	$88.40
Purchase #4	$248.79	5.260%	$261.8764	$261.88	$261.90	$261.90
Purchase #5	$60.72	3.740%	$62.9909	$62.99	$63.00	$63.00
Purchase #6	$155.88	5.534%	$164.5064	$164.51	$164.50	$164.50
Purchase #7	$133.44	4.452%	$139.3807	$139.38	$139.40	$139.40
7 purchase totals =	$880.01		$928.0773	$928.08	$928.10	$928.10