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	$189.86	12.575%	$213.7349	$213.73	$213.75	$213.70
Purchase #2	$144.64	6.536%	$154.0937	$154.09	$154.10	$154.10
Purchase #3	$23.58	8.588%	$25.6051	$25.61	$25.60	$25.60
Purchase #4	$46.67	12.681%	$52.5882	$52.59	$52.60	$52.60
Purchase #5	$74.61	4.767%	$78.1667	$78.17	$78.15	$78.20
Purchase #6	$86.56	4.390%	$90.36	$90.36	$90.35	$90.40
Purchase #7	$41.96	8.456%	$45.5081	$45.51	$45.50	$45.50
7 purchase totals =	$607.88		$660.0567	$660.06	$660.05	$660.10