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	$123.73	12.603%	$139.3237	$139.32	$139.30	$139.30
Purchase #2	$132.71	10.376%	$146.48	$146.48	$146.50	$146.50
Purchase #3	$146.50	9.106%	$159.8403	$159.84	$159.85	$159.80
Purchase #4	$206.39	12.126%	$231.4169	$231.42	$231.40	$231.40
Purchase #5	$176.69	4.322%	$184.3265	$184.33	$184.35	$184.30
Purchase #6	$37.86	4.372%	$39.5152	$39.52	$39.50	$39.50
Purchase #7	$132.68	13.300%	$150.3264	$150.33	$150.35	$150.30
7 purchase totals =	$956.56		$1,051.2290	$1,051.24	$1,051.25	$1,051.10