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	$7.82	3.461%	$8.0907	$8.09	$8.10	$8.10
Purchase #2	$109.37	4.580%	$114.3791	$114.38	$114.40	$114.40
Purchase #3	$210.38	5.812%	$222.6073	$222.61	$222.60	$222.60
Purchase #4	$101.86	9.141%	$111.171	$111.17	$111.15	$111.20
Purchase #5	$158.44	8.331%	$171.6396	$171.64	$171.65	$171.60
Purchase #6	$67.45	11.311%	$75.0793	$75.08	$75.10	$75.10
Purchase #7	$132.45	3.693%	$137.3414	$137.34	$137.35	$137.30
7 purchase totals =	$787.77		$840.3084	$840.31	$840.35	$840.30