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	$136.46	11.591%	$152.2771	$152.28	$152.30	$152.30
Purchase #2	$235.66	10.281%	$259.8882	$259.89	$259.90	$259.90
Purchase #3	$217.52	4.566%	$227.452	$227.45	$227.45	$227.50
Purchase #4	$10.50	12.650%	$11.8283	$11.83	$11.85	$11.80
Purchase #5	$150.50	6.778%	$160.7009	$160.70	$160.70	$160.70
Purchase #6	$247.67	11.558%	$276.2957	$276.30	$276.30	$276.30
Purchase #7	$132.41	3.858%	$137.5184	$137.52	$137.50	$137.50
7 purchase totals =	$1,130.72		$1,225.9606	$1,225.97	$1,226.00	$1,226.00