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	$80.74	5.279%	$85.0023	$85.00	$85.00	$85.00
Purchase #2	$180.43	12.194%	$202.4316	$202.43	$202.45	$202.40
Purchase #3	$225.47	4.712%	$236.0941	$236.09	$236.10	$236.10
Purchase #4	$103.78	8.189%	$112.2785	$112.28	$112.30	$112.30
Purchase #5	$146.77	3.255%	$151.5474	$151.55	$151.55	$151.50
Purchase #6	$33.65	12.745%	$37.9387	$37.94	$37.95	$37.90
Purchase #7	$207.54	11.626%	$231.6686	$231.67	$231.65	$231.70
7 purchase totals =	$978.38		$1,056.9612	$1,056.96	$1,057.00	$1,056.90