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	$90.31	10.773%	$100.0391	$100.04	$100.05	$100.00
Purchase #2	$209.63	5.414%	$220.9794	$220.98	$221.00	$221.00
Purchase #3	$117.74	7.534%	$126.6105	$126.61	$126.60	$126.60
Purchase #4	$219.59	12.692%	$247.4604	$247.46	$247.45	$247.50
Purchase #5	$223.70	7.548%	$240.5849	$240.58	$240.60	$240.60
Purchase #6	$38.68	5.653%	$40.8666	$40.87	$40.85	$40.90
Purchase #7	$169.45	5.601%	$178.9409	$178.94	$178.95	$178.90
7 purchase totals =	$1,069.10		$1,155.4818	$1,155.48	$1,155.50	$1,155.50