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	$91.87	11.261%	$102.2155	$102.22	$102.20	$102.20
Purchase #2	$166.39	9.614%	$182.3867	$182.39	$182.40	$182.40
Purchase #3	$70.45	8.650%	$76.5439	$76.54	$76.55	$76.50
Purchase #4	$155.31	8.863%	$169.0751	$169.08	$169.10	$169.10
Purchase #5	$118.96	7.411%	$127.7761	$127.78	$127.80	$127.80
Purchase #6	$250.82	3.587%	$259.8169	$259.82	$259.80	$259.80
Purchase #7	$59.39	3.455%	$61.4419	$61.44	$61.45	$61.40
7 purchase totals =	$913.19		$979.2561	$979.27	$979.30	$979.20