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	$101.54	5.851%	$107.4811	$107.48	$107.50	$107.50
Purchase #2	$109.55	3.695%	$113.5979	$113.60	$113.60	$113.60
Purchase #3	$57.35	8.653%	$62.3125	$62.31	$62.30	$62.30
Purchase #4	$139.47	10.389%	$153.9595	$153.96	$153.95	$154.00
Purchase #5	$99.30	12.833%	$112.0432	$112.04	$112.05	$112.00
Purchase #6	$237.78	6.846%	$254.0584	$254.06	$254.05	$254.10
Purchase #7	$18.89	13.664%	$21.4711	$21.47	$21.45	$21.50
7 purchase totals =	$763.88		$824.9237	$824.92	$824.90	$825.00