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	$35.43	12.637%	$39.9073	$39.91	$39.90	$39.90
Purchase #2	$11.84	4.854%	$12.4147	$12.41	$12.40	$12.40
Purchase #3	$220.41	11.656%	$246.101	$246.10	$246.10	$246.10
Purchase #4	$231.49	4.267%	$241.3677	$241.37	$241.35	$241.40
Purchase #5	$129.85	8.807%	$141.2859	$141.29	$141.30	$141.30
Purchase #6	$165.32	7.745%	$178.124	$178.12	$178.10	$178.10
Purchase #7	$144.31	8.726%	$156.9025	$156.90	$156.90	$156.90
7 purchase totals =	$938.65		$1,016.1031	$1,016.10	$1,016.05	$1,016.10