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	$95.50	4.487%	$99.7851	$99.79	$99.80	$99.80
Purchase #2	$154.99	7.401%	$166.4608	$166.46	$166.45	$166.50
Purchase #3	$70.49	11.855%	$78.8466	$78.85	$78.85	$78.80
Purchase #4	$124.30	10.184%	$136.9587	$136.96	$136.95	$137.00
Purchase #5	$172.99	8.547%	$187.7755	$187.78	$187.80	$187.80
Purchase #6	$220.88	4.706%	$231.2746	$231.27	$231.25	$231.30
Purchase #7	$69.27	6.440%	$73.731	$73.73	$73.75	$73.70
7 purchase totals =	$908.42		$974.8323	$974.84	$974.85	$974.90