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	$237.94	7.689%	$256.2352	$256.24	$256.25	$256.20
Purchase #2	$201.78	9.756%	$221.4657	$221.47	$221.45	$221.50
Purchase #3	$215.58	12.462%	$242.4456	$242.45	$242.45	$242.40
Purchase #4	$198.59	6.468%	$211.4348	$211.43	$211.45	$211.40
Purchase #5	$65.33	3.273%	$67.4683	$67.47	$67.45	$67.50
Purchase #6	$177.45	4.739%	$185.8594	$185.86	$185.85	$185.90
Purchase #7	$47.25	9.658%	$51.8134	$51.81	$51.80	$51.80
7 purchase totals =	$1,143.92		$1,236.7224	$1,236.73	$1,236.70	$1,236.70