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	$128.91	8.119%	$139.3762	$139.38	$139.40	$139.40
Purchase #2	$120.72	8.564%	$131.0585	$131.06	$131.05	$131.10
Purchase #3	$220.77	13.271%	$250.0684	$250.07	$250.05	$250.10
Purchase #4	$234.96	11.548%	$262.0932	$262.09	$262.10	$262.10
Purchase #5	$92.47	9.178%	$100.9569	$100.96	$100.95	$101.00
Purchase #6	$55.90	3.581%	$57.9018	$57.90	$57.90	$57.90
Purchase #7	$246.28	5.188%	$259.057	$259.06	$259.05	$259.10
7 purchase totals =	$1,100.01		$1,200.5120	$1,200.52	$1,200.50	$1,200.70