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	$106.59	11.341%	$118.6784	$118.68	$118.70	$118.70
Purchase #2	$18.83	9.675%	$20.6518	$20.65	$20.65	$20.70
Purchase #3	$38.41	8.392%	$41.6334	$41.63	$41.65	$41.60
Purchase #4	$70.36	11.191%	$78.234	$78.23	$78.25	$78.20
Purchase #5	$102.61	8.752%	$111.5904	$111.59	$111.60	$111.60
Purchase #6	$119.86	13.505%	$136.0471	$136.05	$136.05	$136.00
Purchase #7	$39.26	3.286%	$40.5501	$40.55	$40.55	$40.60
7 purchase totals =	$495.92		$547.3852	$547.38	$547.45	$547.40