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	$14.48	7.111%	$15.5097	$15.51	$15.50	$15.50
Purchase #2	$154.97	10.801%	$171.7083	$171.71	$171.70	$171.70
Purchase #3	$105.54	13.503%	$119.7911	$119.79	$119.80	$119.80
Purchase #4	$248.26	12.857%	$280.1788	$280.18	$280.20	$280.20
Purchase #5	$157.32	10.667%	$174.1013	$174.10	$174.10	$174.10
Purchase #6	$233.58	8.384%	$253.1633	$253.16	$253.15	$253.20
Purchase #7	$53.28	6.690%	$56.8444	$56.84	$56.85	$56.80
7 purchase totals =	$967.43		$1,071.2969	$1,071.29	$1,071.30	$1,071.30