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	$112.40	9.874%	$123.4984	$123.50	$123.50	$123.50
Purchase #2	$100.67	10.658%	$111.3994	$111.40	$111.40	$111.40
Purchase #3	$17.55	9.566%	$19.2288	$19.23	$19.25	$19.20
Purchase #4	$46.93	4.781%	$49.1737	$49.17	$49.15	$49.20
Purchase #5	$62.38	13.678%	$70.9123	$70.91	$70.90	$70.90
Purchase #6	$25.78	11.693%	$28.7945	$28.79	$28.80	$28.80
Purchase #7	$101.94	6.484%	$108.5498	$108.55	$108.55	$108.50
7 purchase totals =	$467.65		$511.5569	$511.55	$511.55	$511.50