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	$6.25	10.118%	$6.8824	$6.88	$6.90	$6.90
Purchase #2	$86.47	6.229%	$91.8562	$91.86	$91.85	$91.90
Purchase #3	$171.59	5.376%	$180.8147	$180.81	$180.80	$180.80
Purchase #4	$230.69	3.864%	$239.6039	$239.60	$239.60	$239.60
Purchase #5	$91.62	9.786%	$100.5859	$100.59	$100.60	$100.60
Purchase #6	$159.30	3.585%	$165.0109	$165.01	$165.00	$165.00
Purchase #7	$116.94	12.757%	$131.858	$131.86	$131.85	$131.90
7 purchase totals =	$862.86		$916.6120	$916.61	$916.60	$916.70