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	$242.75	13.720%	$276.0553	$276.06	$276.05	$276.10
Purchase #2	$85.89	10.261%	$94.7032	$94.70	$94.70	$94.70
Purchase #3	$121.76	5.742%	$128.7515	$128.75	$128.75	$128.80
Purchase #4	$98.78	13.238%	$111.8565	$111.86	$111.85	$111.90
Purchase #5	$44.53	4.738%	$46.6398	$46.64	$46.65	$46.60
Purchase #6	$53.89	10.842%	$59.7328	$59.73	$59.75	$59.70
Purchase #7	$10.25	5.410%	$10.8045	$10.80	$10.80	$10.80
7 purchase totals =	$657.85		$728.5436	$728.54	$728.55	$728.60