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	$17.61	6.703%	$18.7904	$18.79	$18.80	$18.80
Purchase #2	$216.83	13.226%	$245.5079	$245.51	$245.50	$245.50
Purchase #3	$156.87	7.308%	$168.3341	$168.33	$168.35	$168.30
Purchase #4	$182.56	8.778%	$198.5851	$198.59	$198.60	$198.60
Purchase #5	$204.69	6.758%	$218.523	$218.52	$218.50	$218.50
Purchase #6	$162.25	3.852%	$168.4999	$168.50	$168.50	$168.50
Purchase #7	$70.59	12.528%	$79.4335	$79.43	$79.45	$79.40
7 purchase totals =	$1,011.40		$1,097.6739	$1,097.67	$1,097.70	$1,097.60