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	$159.26	5.464%	$167.962	$167.96	$167.95	$168.00
Purchase #2	$237.36	10.731%	$262.8311	$262.83	$262.85	$262.80
Purchase #3	$86.34	6.637%	$92.0704	$92.07	$92.05	$92.10
Purchase #4	$100.65	12.195%	$112.9243	$112.92	$112.90	$112.90
Purchase #5	$144.80	12.410%	$162.7697	$162.77	$162.75	$162.80
Purchase #6	$94.46	10.371%	$104.2564	$104.26	$104.25	$104.30
Purchase #7	$35.56	7.104%	$38.0862	$38.09	$38.10	$38.10
7 purchase totals =	$858.43		$940.9001	$940.90	$940.85	$941.00