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	$172.88	7.226%	$185.3723	$185.37	$185.35	$185.40
Purchase #2	$213.55	4.297%	$222.7262	$222.73	$222.75	$222.70
Purchase #3	$209.46	5.656%	$221.3071	$221.31	$221.30	$221.30
Purchase #4	$116.66	5.801%	$123.4274	$123.43	$123.45	$123.40
Purchase #5	$107.27	8.554%	$116.4459	$116.45	$116.45	$116.40
Purchase #6	$217.32	10.420%	$239.9647	$239.96	$239.95	$240.00
Purchase #7	$157.83	10.439%	$174.3059	$174.31	$174.30	$174.30
7 purchase totals =	$1,194.97		$1,283.5495	$1,283.56	$1,283.55	$1,283.50