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	$38.83	7.410%	$41.7073	$41.71	$41.70	$41.70
Purchase #2	$59.45	5.591%	$62.7738	$62.77	$62.75	$62.80
Purchase #3	$11.86	10.311%	$13.0829	$13.08	$13.10	$13.10
Purchase #4	$197.70	12.383%	$222.1812	$222.18	$222.20	$222.20
Purchase #5	$20.72	5.272%	$21.8124	$21.81	$21.80	$21.80
Purchase #6	$50.61	7.649%	$54.4812	$54.48	$54.50	$54.50
Purchase #7	$245.44	13.270%	$278.0099	$278.01	$278.00	$278.00
7 purchase totals =	$624.61		$694.0487	$694.04	$694.05	$694.10