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	$18.46	11.579%	$20.5975	$20.60	$20.60	$20.60
Purchase #2	$129.46	9.585%	$141.8687	$141.87	$141.85	$141.90
Purchase #3	$237.44	8.783%	$258.2944	$258.29	$258.30	$258.30
Purchase #4	$135.89	4.531%	$142.0472	$142.05	$142.05	$142.00
Purchase #5	$202.82	4.713%	$212.3789	$212.38	$212.40	$212.40
Purchase #6	$127.64	10.862%	$141.5043	$141.50	$141.50	$141.50
Purchase #7	$25.48	11.412%	$28.3878	$28.39	$28.40	$28.40
7 purchase totals =	$877.19		$945.0788	$945.08	$945.10	$945.10