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	$246.31	13.712%	$280.084	$280.08	$280.10	$280.10
Purchase #2	$213.81	13.808%	$243.3329	$243.33	$243.35	$243.30
Purchase #3	$57.56	7.796%	$62.0474	$62.05	$62.05	$62.00
Purchase #4	$77.88	12.761%	$87.8183	$87.82	$87.80	$87.80
Purchase #5	$135.62	7.372%	$145.6179	$145.62	$145.60	$145.60
Purchase #6	$60.91	9.760%	$66.8548	$66.85	$66.85	$66.90
Purchase #7	$128.76	8.409%	$139.5874	$139.59	$139.60	$139.60
7 purchase totals =	$920.85		$1,025.3427	$1,025.34	$1,025.35	$1,025.30