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	$95.64	9.539%	$104.7631	$104.76	$104.75	$104.80
Purchase #2	$16.82	10.124%	$18.5229	$18.52	$18.50	$18.50
Purchase #3	$245.63	12.221%	$275.6484	$275.65	$275.65	$275.60
Purchase #4	$173.73	6.587%	$185.1736	$185.17	$185.15	$185.20
Purchase #5	$62.68	8.455%	$67.9796	$67.98	$68.00	$68.00
Purchase #6	$73.46	12.419%	$82.583	$82.58	$82.60	$82.60
Purchase #7	$109.45	12.549%	$123.1849	$123.18	$123.20	$123.20
7 purchase totals =	$777.41		$857.8555	$857.84	$857.85	$857.90