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	$11.37	4.337%	$11.8631	$11.86	$11.85	$11.90
Purchase #2	$170.40	12.524%	$191.7409	$191.74	$191.75	$191.70
Purchase #3	$19.97	7.567%	$21.4811	$21.48	$21.50	$21.50
Purchase #4	$178.97	3.240%	$184.7686	$184.77	$184.75	$184.80
Purchase #5	$39.42	3.460%	$40.7839	$40.78	$40.80	$40.80
Purchase #6	$135.87	5.525%	$143.3768	$143.38	$143.40	$143.40
Purchase #7	$41.59	9.856%	$45.6891	$45.69	$45.70	$45.70
7 purchase totals =	$597.59		$639.7035	$639.70	$639.75	$639.80