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	$83.38	8.682%	$90.6191	$90.62	$90.60	$90.60
Purchase #2	$238.57	4.704%	$249.7923	$249.79	$249.80	$249.80
Purchase #3	$107.48	3.707%	$111.4643	$111.46	$111.45	$111.50
Purchase #4	$250.26	12.287%	$281.0094	$281.01	$281.00	$281.00
Purchase #5	$77.46	6.796%	$82.7242	$82.72	$82.70	$82.70
Purchase #6	$131.51	11.186%	$146.2207	$146.22	$146.20	$146.20
Purchase #7	$210.42	13.850%	$239.5632	$239.56	$239.55	$239.60
7 purchase totals =	$1,099.08		$1,201.3932	$1,201.38	$1,201.30	$1,201.40