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	$176.93	6.607%	$188.6198	$188.62	$188.60	$188.60
Purchase #2	$189.37	11.426%	$211.0074	$211.01	$211.00	$211.00
Purchase #3	$37.87	8.180%	$40.9678	$40.97	$40.95	$41.00
Purchase #4	$160.52	7.694%	$172.8704	$172.87	$172.85	$172.90
Purchase #5	$36.61	11.602%	$40.8575	$40.86	$40.85	$40.90
Purchase #6	$227.51	10.140%	$250.5795	$250.58	$250.60	$250.60
Purchase #7	$239.41	9.716%	$262.6711	$262.67	$262.65	$262.70
7 purchase totals =	$1,068.22		$1,167.5735	$1,167.58	$1,167.50	$1,167.70