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	$123.67	12.841%	$139.5505	$139.55	$139.55	$139.60
Purchase #2	$41.33	5.302%	$43.5213	$43.52	$43.50	$43.50
Purchase #3	$115.30	6.745%	$123.077	$123.08	$123.10	$123.10
Purchase #4	$78.54	11.686%	$87.7182	$87.72	$87.70	$87.70
Purchase #5	$69.25	4.411%	$72.3046	$72.30	$72.30	$72.30
Purchase #6	$140.47	7.338%	$150.7777	$150.78	$150.80	$150.80
Purchase #7	$203.98	11.337%	$227.1052	$227.11	$227.10	$227.10
7 purchase totals =	$772.54		$844.0545	$844.06	$844.05	$844.10