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	$18.41	12.547%	$20.7199	$20.72	$20.70	$20.70
Purchase #2	$248.87	10.608%	$275.2701	$275.27	$275.25	$275.30
Purchase #3	$71.33	12.725%	$80.4067	$80.41	$80.40	$80.40
Purchase #4	$129.28	6.626%	$137.8461	$137.85	$137.85	$137.80
Purchase #5	$162.67	12.254%	$182.6036	$182.60	$182.60	$182.60
Purchase #6	$122.30	12.504%	$137.5924	$137.59	$137.60	$137.60
Purchase #7	$25.85	6.187%	$27.4493	$27.45	$27.45	$27.40
7 purchase totals =	$778.71		$861.8881	$861.89	$861.85	$861.80