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	$29.34	13.455%	$33.2877	$33.29	$33.30	$33.30
Purchase #2	$130.64	8.373%	$141.5785	$141.58	$141.60	$141.60
Purchase #3	$84.94	4.681%	$88.916	$88.92	$88.90	$88.90
Purchase #4	$48.72	8.467%	$52.8451	$52.85	$52.85	$52.80
Purchase #5	$38.70	12.261%	$43.445	$43.45	$43.45	$43.40
Purchase #6	$58.38	7.340%	$62.6651	$62.67	$62.65	$62.70
Purchase #7	$133.75	10.123%	$147.2895	$147.29	$147.30	$147.30
7 purchase totals =	$524.47		$570.0269	$570.05	$570.05	$570.00