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	$244.84	10.423%	$270.3597	$270.36	$270.35	$270.40
Purchase #2	$226.64	12.750%	$255.5366	$255.54	$255.55	$255.50
Purchase #3	$61.71	9.792%	$67.7526	$67.75	$67.75	$67.80
Purchase #4	$222.60	7.521%	$239.3417	$239.34	$239.35	$239.30
Purchase #5	$155.28	8.692%	$168.7769	$168.78	$168.80	$168.80
Purchase #6	$38.88	6.443%	$41.385	$41.39	$41.40	$41.40
Purchase #7	$32.66	12.184%	$36.6393	$36.64	$36.65	$36.60
7 purchase totals =	$982.61		$1,079.7918	$1,079.80	$1,079.85	$1,079.80