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	$89.47	12.424%	$100.5858	$100.59	$100.60	$100.60
Purchase #2	$105.82	3.320%	$109.3332	$109.33	$109.35	$109.30
Purchase #3	$155.76	6.551%	$165.9638	$165.96	$165.95	$166.00
Purchase #4	$217.79	7.687%	$234.5315	$234.53	$234.55	$234.50
Purchase #5	$182.87	11.265%	$203.4703	$203.47	$203.45	$203.50
Purchase #6	$73.85	10.537%	$81.6316	$81.63	$81.65	$81.60
Purchase #7	$148.47	12.105%	$166.4423	$166.44	$166.45	$166.40
7 purchase totals =	$974.03		$1,061.9585	$1,061.95	$1,062.00	$1,061.90