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	$171.46	6.644%	$182.8518	$182.85	$182.85	$182.90
Purchase #2	$88.95	11.656%	$99.318	$99.32	$99.30	$99.30
Purchase #3	$92.54	7.495%	$99.4759	$99.48	$99.50	$99.50
Purchase #4	$15.57	11.357%	$17.3383	$17.34	$17.35	$17.30
Purchase #5	$90.38	13.452%	$102.5379	$102.54	$102.55	$102.50
Purchase #6	$124.95	9.360%	$136.6453	$136.65	$136.65	$136.60
Purchase #7	$126.55	10.180%	$139.4328	$139.43	$139.45	$139.40
7 purchase totals =	$710.40		$777.6000	$777.61	$777.65	$777.50