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	$35.79	13.499%	$40.6213	$40.62	$40.60	$40.60
Purchase #2	$18.71	11.526%	$20.8665	$20.87	$20.85	$20.90
Purchase #3	$161.99	8.399%	$175.5955	$175.60	$175.60	$175.60
Purchase #4	$198.40	11.541%	$221.2973	$221.30	$221.30	$221.30
Purchase #5	$184.84	6.131%	$196.1725	$196.17	$196.15	$196.20
Purchase #6	$104.81	6.707%	$111.8396	$111.84	$111.85	$111.80
Purchase #7	$215.88	3.724%	$223.9194	$223.92	$223.90	$223.90
7 purchase totals =	$920.42		$990.3121	$990.32	$990.25	$990.30