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	$128.97	5.870%	$136.5405	$136.54	$136.55	$136.50
Purchase #2	$101.32	4.237%	$105.6129	$105.61	$105.60	$105.60
Purchase #3	$138.82	6.446%	$147.7683	$147.77	$147.75	$147.80
Purchase #4	$127.78	9.618%	$140.0699	$140.07	$140.05	$140.10
Purchase #5	$199.40	9.353%	$218.0499	$218.05	$218.05	$218.00
Purchase #6	$154.29	11.863%	$172.5934	$172.59	$172.60	$172.60
Purchase #7	$109.31	12.764%	$123.2623	$123.26	$123.25	$123.30
7 purchase totals =	$959.89		$1,043.8972	$1,043.89	$1,043.85	$1,043.90