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	$5.38	7.852%	$5.8024	$5.80	$5.80	$5.80
Purchase #2	$168.56	6.726%	$179.8973	$179.90	$179.90	$179.90
Purchase #3	$151.27	7.558%	$162.703	$162.70	$162.70	$162.70
Purchase #4	$146.69	13.768%	$166.8863	$166.89	$166.90	$166.90
Purchase #5	$81.74	9.536%	$89.5347	$89.53	$89.55	$89.50
Purchase #6	$20.52	4.348%	$21.4122	$21.41	$21.40	$21.40
Purchase #7	$62.59	8.262%	$67.7612	$67.76	$67.75	$67.80
7 purchase totals =	$636.75		$693.9971	$693.99	$694.00	$694.00