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	$40.59	7.226%	$43.523	$43.52	$43.50	$43.50
Purchase #2	$48.44	5.291%	$51.003	$51.00	$51.00	$51.00
Purchase #3	$18.30	11.557%	$20.4149	$20.41	$20.40	$20.40
Purchase #4	$59.72	8.538%	$64.8189	$64.82	$64.80	$64.80
Purchase #5	$249.44	8.832%	$271.4705	$271.47	$271.45	$271.50
Purchase #6	$198.64	3.790%	$206.1685	$206.17	$206.15	$206.20
Purchase #7	$47.45	12.481%	$53.3722	$53.37	$53.35	$53.40
7 purchase totals =	$662.58		$710.7710	$710.76	$710.65	$710.80