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	$34.48	11.526%	$38.4542	$38.45	$38.45	$38.50
Purchase #2	$215.83	9.565%	$236.4741	$236.47	$236.45	$236.50
Purchase #3	$217.44	7.424%	$233.5827	$233.58	$233.60	$233.60
Purchase #4	$109.79	12.506%	$123.5203	$123.52	$123.50	$123.50
Purchase #5	$228.96	9.180%	$249.9785	$249.98	$250.00	$250.00
Purchase #6	$81.68	11.167%	$90.8012	$90.80	$90.80	$90.80
Purchase #7	$138.44	6.129%	$146.925	$146.93	$146.95	$146.90
7 purchase totals =	$1,026.62		$1,119.7360	$1,119.73	$1,119.75	$1,119.80