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	$92.63	7.309%	$99.4003	$99.40	$99.40	$99.40
Purchase #2	$112.51	13.851%	$128.0938	$128.09	$128.10	$128.10
Purchase #3	$46.77	7.626%	$50.3367	$50.34	$50.35	$50.30
Purchase #4	$202.50	11.730%	$226.2533	$226.25	$226.25	$226.30
Purchase #5	$73.88	3.662%	$76.5855	$76.59	$76.60	$76.60
Purchase #6	$77.75	3.819%	$80.7193	$80.72	$80.70	$80.70
Purchase #7	$113.56	3.488%	$117.521	$117.52	$117.50	$117.50
7 purchase totals =	$719.60		$778.9099	$778.91	$778.90	$778.90