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	$215.86	12.352%	$242.523	$242.52	$242.50	$242.50
Purchase #2	$171.30	4.499%	$179.0068	$179.01	$179.00	$179.00
Purchase #3	$70.48	3.306%	$72.8101	$72.81	$72.80	$72.80
Purchase #4	$166.52	11.286%	$185.3134	$185.31	$185.30	$185.30
Purchase #5	$160.52	8.405%	$174.0117	$174.01	$174.00	$174.00
Purchase #6	$194.91	11.833%	$217.9737	$217.97	$217.95	$218.00
Purchase #7	$237.87	11.683%	$265.6604	$265.66	$265.65	$265.70
7 purchase totals =	$1,217.46		$1,337.2991	$1,337.29	$1,337.20	$1,337.30