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	$203.66	13.715%	$231.592	$231.59	$231.60	$231.60
Purchase #2	$80.77	10.724%	$89.4318	$89.43	$89.45	$89.40
Purchase #3	$154.41	13.136%	$174.6933	$174.69	$174.70	$174.70
Purchase #4	$91.93	7.247%	$98.5922	$98.59	$98.60	$98.60
Purchase #5	$39.87	3.854%	$41.4066	$41.41	$41.40	$41.40
Purchase #6	$146.91	5.366%	$154.7932	$154.79	$154.80	$154.80
Purchase #7	$33.88	3.805%	$35.1691	$35.17	$35.15	$35.20
7 purchase totals =	$751.43		$825.6782	$825.67	$825.70	$825.70