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	$194.47	11.273%	$216.3926	$216.39	$216.40	$216.40
Purchase #2	$102.71	8.578%	$111.5205	$111.52	$111.50	$111.50
Purchase #3	$189.74	6.756%	$202.5588	$202.56	$202.55	$202.60
Purchase #4	$226.77	8.813%	$246.7552	$246.76	$246.75	$246.80
Purchase #5	$116.56	12.834%	$131.5193	$131.52	$131.50	$131.50
Purchase #6	$197.45	11.485%	$220.1271	$220.13	$220.15	$220.10
Purchase #7	$61.83	13.225%	$70.007	$70.01	$70.00	$70.00
7 purchase totals =	$1,089.53		$1,198.8805	$1,198.89	$1,198.85	$1,198.90