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	$16.81	3.698%	$17.4316	$17.43	$17.45	$17.40
Purchase #2	$79.77	13.444%	$90.4943	$90.49	$90.50	$90.50
Purchase #3	$46.83	4.746%	$49.0526	$49.05	$49.05	$49.10
Purchase #4	$64.93	9.171%	$70.8847	$70.88	$70.90	$70.90
Purchase #5	$153.96	11.230%	$171.2497	$171.25	$171.25	$171.20
Purchase #6	$73.25	6.834%	$78.2559	$78.26	$78.25	$78.30
Purchase #7	$35.96	12.441%	$40.4338	$40.43	$40.45	$40.40
7 purchase totals =	$471.51		$517.8026	$517.79	$517.85	$517.80