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	$108.52	9.122%	$118.4192	$118.42	$118.40	$118.40
Purchase #2	$43.55	3.155%	$44.924	$44.92	$44.90	$44.90
Purchase #3	$51.69	8.178%	$55.9172	$55.92	$55.90	$55.90
Purchase #4	$113.34	13.462%	$128.5978	$128.60	$128.60	$128.60
Purchase #5	$64.80	10.417%	$71.5502	$71.55	$71.55	$71.60
Purchase #6	$160.92	9.393%	$176.0352	$176.04	$176.05	$176.00
Purchase #7	$238.38	13.634%	$270.8807	$270.88	$270.90	$270.90
7 purchase totals =	$781.20		$866.3243	$866.33	$866.30	$866.30