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	$36.32	10.158%	$40.0094	$40.01	$40.00	$40.00
Purchase #2	$227.37	4.177%	$236.8672	$236.87	$236.85	$236.90
Purchase #3	$122.39	3.842%	$127.0922	$127.09	$127.10	$127.10
Purchase #4	$221.26	7.712%	$238.3236	$238.32	$238.30	$238.30
Purchase #5	$224.45	5.818%	$237.5085	$237.51	$237.50	$237.50
Purchase #6	$232.73	7.675%	$250.592	$250.59	$250.60	$250.60
Purchase #7	$154.26	5.190%	$162.2661	$162.27	$162.25	$162.30
7 purchase totals =	$1,218.78		$1,292.6590	$1,292.66	$1,292.60	$1,292.70