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	$133.60	3.320%	$138.0355	$138.04	$138.05	$138.00
Purchase #2	$247.45	4.640%	$258.9317	$258.93	$258.95	$258.90
Purchase #3	$124.66	13.740%	$141.7883	$141.79	$141.80	$141.80
Purchase #4	$246.59	13.871%	$280.7945	$280.79	$280.80	$280.80
Purchase #5	$224.59	7.507%	$241.45	$241.45	$241.45	$241.50
Purchase #6	$61.76	9.580%	$67.6766	$67.68	$67.70	$67.70
Purchase #7	$31.37	13.501%	$35.6053	$35.61	$35.60	$35.60
7 purchase totals =	$1,070.02		$1,164.2819	$1,164.29	$1,164.35	$1,164.30