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	$87.33	3.700%	$90.5612	$90.56	$90.55	$90.60
Purchase #2	$103.50	12.526%	$116.4644	$116.46	$116.45	$116.50
Purchase #3	$165.72	13.209%	$187.61	$187.61	$187.60	$187.60
Purchase #4	$69.83	12.419%	$78.5022	$78.50	$78.50	$78.50
Purchase #5	$223.30	6.246%	$237.2473	$237.25	$237.25	$237.20
Purchase #6	$131.36	3.743%	$136.2768	$136.28	$136.30	$136.30
Purchase #7	$107.40	4.843%	$112.6014	$112.60	$112.60	$112.60
7 purchase totals =	$888.44		$959.2633	$959.26	$959.25	$959.30