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	$100.56	10.587%	$111.2063	$111.21	$111.20	$111.20
Purchase #2	$217.39	4.675%	$227.553	$227.55	$227.55	$227.60
Purchase #3	$198.41	9.633%	$217.5228	$217.52	$217.50	$217.50
Purchase #4	$204.68	11.322%	$227.8539	$227.85	$227.85	$227.90
Purchase #5	$175.73	8.365%	$190.4298	$190.43	$190.45	$190.40
Purchase #6	$198.46	5.642%	$209.6571	$209.66	$209.65	$209.70
Purchase #7	$110.74	5.231%	$116.5328	$116.53	$116.55	$116.50
7 purchase totals =	$1,205.97		$1,300.7557	$1,300.75	$1,300.75	$1,300.80