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	$37.54	7.436%	$40.3315	$40.33	$40.35	$40.30
Purchase #2	$11.70	8.266%	$12.6671	$12.67	$12.65	$12.70
Purchase #3	$76.41	3.422%	$79.0248	$79.02	$79.00	$79.00
Purchase #4	$101.94	9.326%	$111.4469	$111.45	$111.45	$111.40
Purchase #5	$139.40	12.346%	$156.6103	$156.61	$156.60	$156.60
Purchase #6	$95.37	4.396%	$99.5625	$99.56	$99.55	$99.60
Purchase #7	$172.99	4.591%	$180.932	$180.93	$180.95	$180.90
7 purchase totals =	$635.35		$680.5751	$680.57	$680.55	$680.50