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	$186.27	9.696%	$204.3307	$204.33	$204.35	$204.30
Purchase #2	$101.53	10.773%	$112.4678	$112.47	$112.45	$112.50
Purchase #3	$91.50	13.483%	$103.8369	$103.84	$103.85	$103.80
Purchase #4	$82.71	10.297%	$91.2266	$91.23	$91.25	$91.20
Purchase #5	$210.63	3.233%	$217.4397	$217.44	$217.45	$217.40
Purchase #6	$158.44	5.144%	$166.5902	$166.59	$166.60	$166.60
Purchase #7	$79.49	10.168%	$87.5725	$87.57	$87.55	$87.60
7 purchase totals =	$910.57		$983.4644	$983.47	$983.50	$983.40