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	$87.58	13.126%	$99.0758	$99.08	$99.10	$99.10
Purchase #2	$45.58	11.116%	$50.6467	$50.65	$50.65	$50.60
Purchase #3	$181.38	5.429%	$191.2271	$191.23	$191.25	$191.20
Purchase #4	$35.70	13.495%	$40.5177	$40.52	$40.50	$40.50
Purchase #5	$215.80	12.615%	$243.0232	$243.02	$243.00	$243.00
Purchase #6	$84.75	4.849%	$88.8595	$88.86	$88.85	$88.90
Purchase #7	$164.45	9.828%	$180.6121	$180.61	$180.60	$180.60
7 purchase totals =	$815.24		$893.9621	$893.97	$893.95	$893.90