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	$130.59	13.462%	$148.17	$148.17	$148.15	$148.20
Purchase #2	$209.77	10.152%	$231.0659	$231.07	$231.05	$231.10
Purchase #3	$38.53	7.734%	$41.5099	$41.51	$41.50	$41.50
Purchase #4	$241.88	12.666%	$272.5165	$272.52	$272.50	$272.50
Purchase #5	$247.48	13.466%	$280.8057	$280.81	$280.80	$280.80
Purchase #6	$126.71	3.386%	$131.0004	$131.00	$131.00	$131.00
Purchase #7	$122.78	11.818%	$137.2901	$137.29	$137.30	$137.30
7 purchase totals =	$1,117.74		$1,242.3585	$1,242.37	$1,242.30	$1,242.40