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	$123.32	4.530%	$128.9064	$128.91	$128.90	$128.90
Purchase #2	$158.74	7.750%	$171.0424	$171.04	$171.05	$171.00
Purchase #3	$143.78	13.457%	$163.1285	$163.13	$163.15	$163.10
Purchase #4	$84.98	4.259%	$88.5993	$88.60	$88.60	$88.60
Purchase #5	$225.52	11.145%	$250.6542	$250.65	$250.65	$250.70
Purchase #6	$248.85	12.858%	$280.8471	$280.85	$280.85	$280.80
Purchase #7	$92.51	13.704%	$105.1876	$105.19	$105.20	$105.20
7 purchase totals =	$1,077.70		$1,188.3655	$1,188.37	$1,188.40	$1,188.30