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	$102.51	12.459%	$115.2817	$115.28	$115.30	$115.30
Purchase #2	$208.98	12.261%	$234.603	$234.60	$234.60	$234.60
Purchase #3	$111.52	4.817%	$116.8919	$116.89	$116.90	$116.90
Purchase #4	$217.31	6.565%	$231.5764	$231.58	$231.60	$231.60
Purchase #5	$162.27	11.119%	$180.3128	$180.31	$180.30	$180.30
Purchase #6	$86.81	4.758%	$90.9404	$90.94	$90.95	$90.90
Purchase #7	$84.90	5.395%	$89.4804	$89.48	$89.50	$89.50
7 purchase totals =	$974.30		$1,059.0866	$1,059.08	$1,059.15	$1,059.10