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	$163.57	10.592%	$180.8953	$180.90	$180.90	$180.90
Purchase #2	$117.66	5.188%	$123.7642	$123.76	$123.75	$123.80
Purchase #3	$111.73	10.653%	$123.6326	$123.63	$123.65	$123.60
Purchase #4	$210.54	3.231%	$217.3425	$217.34	$217.35	$217.30
Purchase #5	$161.42	3.211%	$166.6032	$166.60	$166.60	$166.60
Purchase #6	$6.92	6.203%	$7.3492	$7.35	$7.35	$7.30
Purchase #7	$112.39	7.650%	$120.9878	$120.99	$121.00	$121.00
7 purchase totals =	$884.23		$940.5748	$940.57	$940.60	$940.50