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	$94.39	12.224%	$105.9282	$105.93	$105.95	$105.90
Purchase #2	$123.70	13.677%	$140.6184	$140.62	$140.60	$140.60
Purchase #3	$86.86	4.706%	$90.9476	$90.95	$90.95	$90.90
Purchase #4	$25.43	12.470%	$28.6011	$28.60	$28.60	$28.60
Purchase #5	$117.60	6.190%	$124.8794	$124.88	$124.90	$124.90
Purchase #6	$16.35	13.634%	$18.5792	$18.58	$18.60	$18.60
Purchase #7	$169.71	6.395%	$180.563	$180.56	$180.55	$180.60
7 purchase totals =	$634.04		$690.1169	$690.12	$690.15	$690.10